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231 results on '"Gianni Bernardi"'

51. KAT-7 observations of an unbiased sample of mass-selected galaxy clusters

Author: V. Cuciti, Viral Parekh, Daniele Dallacasa, Gianni Bernardi, Tiziana Venturi, Rossella Cassano, Gianfranco Brunetti, Melanie Johnston-Hollitt, Nadeem Oozeer, Oleg Smirnov, Bernardi, G., Venturi, T., Cassano, R., Dallacasa, D., Brunetti, G., Cuciti, V., Johnston-Hollitt, M., Oozeer, N., Parekh, V., and Smirnov, O.M.
Subjects: Physics, 010308 nuclear & particles physics, Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Radio continuum: galaxie, 01 natural sciences, Radio continuum: general, Galaxy groups and clusters, X-shaped radio galaxy, Radio halo, Space and Planetary Science, Intracluster medium, 0103 physical sciences, Galaxies: clusters: general, Halo, Low Mass, Galaxies: clusters: intracluster medium, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Galaxy cluster
Abstract: The presence of megaparsec-scale radio haloes in galaxy clusters has already been established by many observations over the last two decades. The emerging explanation for the formation of these giant sources of diffuse synchrotron radio emission is that they trace turbulent regions in the intracluster medium, where particles are trapped and accelerated during cluster mergers. Our current observational knowledge is, however, mainly limited to massive systems. Here we present observations of a sample of 14 mass-selected galaxy clusters, I.e. M500 > 4 × 1014 M☉, in the Southern hemisphere, aimed to study the occurrence of radio haloes in low-mass clusters and test the correlation between the radio halo power at 1.4 GHz P1.4 and the cluster mass M500. Our observations were performed with the 7-element Karoo Array Telescope at 1.86 GHz. We found three candidates to host diffuse cluster-scale emission and derived upper limits at the level of 0.6-1.9 × 1024 Watt Hz-1 for ∼50 per cent of the clusters in the sample, significantly increasing the number of clusters with radio halo information in the considered mass range. Our results confirm that bright radio haloes in less massive galaxy clusters are statistically rare.
Published: 2015

52. Measuring HERA's Primary Beam in Situ: Methodology and First Results

Author: Richard F. Bradley, Matthew Kolopanis, Jonathan C. Pober, Andrei Mesinger, Daniel C. Jacobs, Bradley Greig, Jasper Grobbelaar, Cresshim Malgas, Craig Smith, Nicolas Fagnoni, Peter Sims, Yanga Balfour, Joshua Kerrigan, Angelo Syce, Tashalee S. Billings, Zachary E. Martinot, Piyanat Kittiwisit, Aaron R. Parsons, Chuneeta D. Nunhokee, Chris Carilli, Kingsley Gale-Sides, Nicholas S. Kern, Eloy de Lera Acedo, Peter K. G. Williams, Paul Alexander, Eunice Matsetela, Saul A. Kohn, Adam Lanman, Paul La Plante, David DeBoer, Nima Razavi-Ghods, David MacMahon, Bryna J. Hazelton, Nipanjana Patra, Adam P. Beardsley, Jon Ringuette, Matt Dexter, Ziyaad Halday, Deepthi Gorthi, Adrian Liu, Brian Glendenning, Nithyanandan Thyagarajan, Abraham R. Neben, Joshua S. Dillon, Gianni Bernardi, Zara Abdurashidova, Carina Cheng, Lourence Malan, Judd D. Bowman, Randall Fritz, Samantha Pieterse, Jacob Burba, Miguel F. Morales, Austin Julius, Zaki S. Ali, Bojan Nikolic, Aaron Ewall-Wice, James Robnett, Jacqueline N. Hewitt, James E. Aguirre, Kathryn Rosie, Steve R. Furlanetto, Mathakane Molewa, Haoxuan Zheng, Tshegofalang Mosiane, Matthys Maree, Telalo Lekalake, ITA, USA, CAF, Nunhokee, C. D., Parsons, A. R., Kern, N. S., Nikolic, B., Pober, J. C., Bernardi, G., Carilli, C. L., Abdurashidova, Z., Aguirre, J. E., Alexander, P., Ali, Z. S., Balfour, Y., Beardsley, A. P., Billings, T. S., Bowman, J. D., Bradley, R. F., Burba, J., Cheng, C., Deboer, D. R., Dexter, M., Acedo, E. D. L., Dillon, J. S., Ewall-Wice, A., Fagnoni, N., Fritz, R., Furlanetto, S. R., Gale-Sides, K., Glendenning, B., Gorthi, D., Greig, B., Grobbelaar, J., Halday, Z., Hazelton, B. J., Hewitt, J. N., Jacobs, D. C., Julius, A., Kerrigan, J., Kittiwisit, P., Kohn, S. A., Kolopanis, M., Lanman, A., Plante, P. L., Lekalake, T., Liu, A., Macmahon, D., Malan, L., Malgas, C., Maree, M., Martinot, Z. E., Matsetela, E., Mesinger, A., Molewa, M., Morales, M. F., Mosiane, T., Neben, A. R., Patra, N., Pieterse, S., Razavi-Ghods, N., Ringuette, J., Robnett, J., Rosie, K., Sims, P., Smith, C., Syce, A., Thyagarajan, N., Williams, P. K. G., and Zheng, H.
Subjects: In situ, Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, HERA, 01 natural sciences, Cosmology, Nuclear physics, Settore FIS/05 - Astronomia e Astrofisica, Space and Planetary Science, Primary (astronomy), 0103 physical sciences, H I line emission, Radio astronomy, Astrophysics - Instrumentation and Methods for Astrophysics, 010306 general physics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Beam (structure), Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The central challenge in 21~cm cosmology is isolating the cosmological signal from bright foregrounds. Many separation techniques rely on the accurate knowledge of the sky and the instrumental response, including the antenna primary beam. For drift-scan telescopes such as the Hydrogen Epoch of Reionization Array \citep[HERA, ][]{DeBoer2017} that do not move, primary beam characterization is particularly challenging because standard beam-calibration routines do not apply \citep{Cornwell2005} and current techniques require accurate source catalogs at the telescope resolution. We present an extension of the method from \citet{Pober2012} where they use beam symmetries to create a network of overlapping source tracks that break the degeneracy between source flux density and beam response and allow their simultaneous estimation. We fit the beam response of our instrument using early HERA observations and find that our results agree well with electromagnetic simulations down to a -20~dB level in power relative to peak gain for sources with high signal-to-noise ratio. In addition, we construct a source catalog with 90 sources down to a flux density of 1.4~Jy at 151~MHz., 22 pages, 22 figures, accepted for publication in ApJ
Published: 2020

53. The HERA-19 Commissioning Array: Direction-dependent Effects

Author: Judd D. Bowman, Samantha Pieterse, Daniel C. Jacobs, Gcobisa Fadana, Paul M. Chichura, C. H. Smith, Jacqueline N. Hewitt, Richard F. Bradley, Matthew Kolopanis, Joshua S. Dillon, Jon Ringuette, Cresshim Malgas, Jonathan C. Pober, Andrei Mesinger, Nicolas Fagnoni, Jasper Grobbelaar, Chris Carilli, Nima Razavi-Ghods, Tashalee S. Billings, Zachary E. Martinot, Eloy de Lera Acedo, David DeBoer, Chuneeta D. Nunhokee, Miguel F. Morales, Roshan K. Benefo, Haoxuan Zheng, Brian Glendenning, Austin Julius, Amy S. Igarashi, Gianni Bernardi, Carina Cheng, Zaki S. Ali, Nipanjana Patra, Bojan Nikolic, Aaron Ewall-Wice, Anita Loots, Angelo Syce, Peter Williams, Paul Alexander, Lourence Malan, Eunice Matsetela, Nithyanandan Thyagarajan, Steven R. Furlanetto, James E. Aguirre, Raddwine Sell, MacCalvin Kariseb, Telalo Lekalake, Max Tegmark, Matthys Maree, Bryna J. Hazelton, Bradley Greig, Adrian Liu, Jack Hickish, Nicholas S. Kern, Paul La Plante, Abraham R. Neben, Randall Fritz, Aaron R. Parsons, Samavarti Gallardo, Austin F. Fortino, Philip Bull, James Robnett, David MacMahon, Adam P. Beardsley, Saul A. Kohn, Kathryn Rosie, Nathan Mathison, ITA, USA, Kohn, SA [0000-0001-6744-5328], Aguirre, JE [0000-0002-4810-666X], La Plante, P [0000-0002-4693-0102], Nunhokee, CD [0000-0002-5445-6586], Kern, NS [0000-0002-8211-1892], Liu, A [0000-0001-6876-0928], Beardsley, AP [0000-0001-9428-8233], Bernardi, G [0000-0002-0916-7443], Bowman, JD [0000-0002-8475-2036], Carilli, CL [0000-0001-6647-3861], Dillon, JS [0000-0003-3336-9958], Ewall-Wice, A [0000-0002-0086-7363], Furlanetto, SR [0000-0002-0658-1243], Hazelton, BJ [0000-0001-7532-645X], Jacobs, DC [0000-0002-0917-2269], Kolopanis, M [0000-0002-2950-2974], Morales, MF [0000-0001-7694-4030], Neben, AR [0000-0001-7776-7240], Patra, N [0000-0002-9457-1941], Tegmark, M [0000-0001-7670-7190], Thyagarajan, N [0000-0003-1602-7868], Williams, PKG [0000-0003-3734-3587], Apollo - University of Cambridge Repository, Kohn, S. A., Aguirre, J. E., La Plante, P., Billings, T. S., Chichura, P. M., Fortino, A. F., Igarashi, A. S., Benefo, R. K., Gallardo, S., Martinot, Z. E., Nunhokee, C. D., Kern, N. S., Bull, P., Liu, A., Alexander, P., Ali, Z. S., Beardsley, A. P., Bernardi, G., Bowman, J. D., Bradley, R. F., Carilli, C. L., Cheng, C., Deboer, D. R., Acedo, E. D. L., Dillon, J. S., Ewall-Wice, A., Fadana, G., Fagnoni, N., Furlanetto, S. R., Glendenning, B., Greig, B., Grobbelaar, J., Hazelton, B. J., Hewitt, J. N., Hickish, J., Jacobs, D. C., Julius, A., Kariseb, M., Kolopanis, M., Lekalake, T., Loots, A., Macmahon, D., Malan, L., Malgas, C., Maree, M., Mathison, N., Matsetela, E., Mesinger, A., Morales, M. F., Neben, A. R., Nikolic, B., Parsons, A. R., Patra, N., Pieterse, S., Pober, J. C., Randall, F., Razavi-Ghods, N., Ringuette, J., Robnett, J., Rosie, K., Sell, R., Smith, C., Syce, A., Tegmark, M., Thyagarajan, N., Williams, P. K. G., and Zheng, H.
Subjects: 010504 meteorology & atmospheric sciences, interferometers [instrumentation], Atomic, Physical Chemistry, 7. Clean energy, 01 natural sciences, Spectral line, Particle and Plasma Physics, Astronomical interferometer, Stokes parameters, dark ages, instrumentation: interferometers, 010303 astronomy & astrophysics, Physics, Linear polarization, Astrophysics::Instrumentation and Methods for Astrophysics, HERA, Polarization (waves), observations [cosmology], interferometric [techniques], interferometer [instrumentation], Amplitude, techniques: interferometric, symbols, reionization, dark ages, reionization, first star, Astrophysics - Instrumentation and Methods for Astrophysics, Astronomical and Space Sciences, observation [cosmology], Physical Chemistry (incl. Structural), first stars, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astronomy & Astrophysics, symbols.namesake, Settore FIS/05 - Astronomia e Astrofisica, 0103 physical sciences, Nuclear, dark ages, reionization, first stars, Reionization, Instrumentation and Methods for Astrophysics (astro-ph.IM), Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, polarization, 010308 nuclear & particles physics, Molecular, Astronomy and Astrophysics, Computational physics, Space and Planetary Science, 13. Climate action, cosmology: observations, astro-ph.IM
Abstract: Foreground power dominates the measurements of interferometers that seek a statistical detection of highly-redshifted HI emission from the Epoch of Reionization (EoR). The chromaticity of the instrument creates a boundary in the Fourier transform of frequency (proportional to $k_\parallel$) between spectrally smooth emission, characteristic of the strong synchrotron foreground (the "wedge"), and the spectrally structured emission from HI in the EoR (the "EoR window"). Faraday rotation can inject spectral structure into otherwise smooth polarized foreground emission, which through instrument effects or miscalibration could possibly pollute the EoR window. Using data from the HERA 19-element commissioning array, we investigate the polarization response of this new instrument in the power spectrum domain. We perform a simple image-based calibration based on the unpolarized diffuse emission of the Global Sky Model, and show that it achieves qualitative redundancy between the nominally-redundant baselines of the array and reasonable amplitude accuracy. We construct power spectra of all fully polarized coherencies in all pseudo-Stokes parameters. We compare to simulations based on an unpolarized diffuse sky model and detailed electromagnetic simulations of the dish and feed, confirming that in Stokes I, the calibration does not add significant spectral structure beyond the expected level. Further, this calibration is stable over the 8 days of observations considered. Excess power is seen in the power spectra of the linear polarization Stokes parameters which is not easily attributable to leakage via the primary beam, and results from some combination of residual calibration errors and actual polarized emission. Stokes V is found to be highly discrepant from the expectation of zero power, strongly pointing to the need for more accurate polarized calibration., Comment: 21 pages, 12 figures, submitted to ApJ
Published: 2018
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54. Current and future observations of the high-z IGM with the 21cm line

Author: Gianni Bernardi
Subjects: Physics, Astrophysics, Current (fluid), Line (text file)
Published: 2018

55. Measurements of the global 21-cm signal from the Cosmic Dawn

Author: Gianni Bernardi
Subjects: Diffuse radiation, Physics, Range (particle radiation), Cosmology and Nongalactic Astrophysics (astro-ph.CO), COSMIC cancer database, 010308 nuclear & particles physics, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Signal, Space and Planetary Science, Intergalactic medium, 0103 physical sciences, Dark Ages, 010303 astronomy & astrophysics, Reionization, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The sky-averaged (global) 21-cm signal is a very promising probe of the Cosmic Dawn, when the first luminous sources were formed and started to shine in a substantially neutral intergalactic medium. I here report on the status and early result of the Large-Aperture Experiment to Detect the Dark Age that focuses on observations of the global 21-cm signal in the $16 \lesssim z \lesssim 30$ range., Contributed talk to the IAU Symposium 333 "Peering towards Cosmic Dawn", Dubrovnik, October 2-6, 2017; to appear in the proceedings, eds. Vibor Jelic and Thijs van der Hulst [4 pages, 2 figures]
Published: 2018

56. A MeerKAT View on Galaxy Clusters

Author: Gianni Bernardi, Rossella Cassano, Gianfranco Brunetti, S. Makhatini, B. L. Fanaroff, Oleg Smirnov, B. Hugo, Tiziana Venturi, Daniele Dallacasa, Nadeem Oozeer, and Jonathan T. L. Zwart
Subjects: Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Order (ring theory), Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Electron, Relativistic particle, Radio telescope, Radio halo, Cluster (physics), Halo, Astrophysics::Galaxy Astrophysics, Galaxy cluster, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Almost two decades of observations of radio emission in galaxy clusters have proven the existence of relativistic particles and magnetic fields that generate extended synchrotron emission in the form of radio halos. In the current scenario, radio halos are generated through re--acceleration of relativistic electrons by turbulence generated by cluster mergers. Although this theoretical framework has received increasingly supporting observational evidence over the last ten years, observations of statistically complete samples are needed in order to fundamentally test model predictions. In this paper we briefly review our 7--element Karoo Radio Telescope observations of a sample of nearby clusters aimed to test the predictions of the turbulent re--acceleration model in small systems ($M_{500} > 4 \times 10^{14}$ M$_{\odot}$). We conclude by presenting two galaxy cluster surveys to be carried out with MeerKAT in order to provide crucial test of models of radio halo formation in nearby ($z < 0.1$) and high redshift ($z > 0.4$) systems respectively., 7 pages, 2 figures Accepted for publication, Proceedings of Science, Workshop on "MeerKAT Science: On the Pathway to the SKA", held in Stellenbosch 25-27 May, 2016
Published: 2018

57. Revival of the Magnetar PSR J1622-4950:Observations with MeerKAT, Parkes, XMM-Newton, Swift, Chandra, and NuSTAR

Author: G C Du Toit, T. D. Abbott, A. J. T. Ramaila, P. S. Swart, P. Ntuli, G. de Bruin, Stephanie Smith, T. E. Monama, C. Stuart, Andrew Jameson, R. Spann, H. Kriel, N. Matthysen, J. Horrell, K. M. B. Asad, D. H. Botha, L. P. Williams, L. D. Mc Nally, R. T. Lord, A. Struthers, W. de Villiers, H. Niehaus, E. F. Bauermeister, John Sarkissian, B. Jordaan, R. Andreas, T. G. H. Bennett, J. P. Conradie, Riana Geschke, I. Wait, B. Ngcebetsha, A. van der Byl, Ben Stappers, A. Robyntjies, J. P. Jansen van Rensburg, N. Mabombo, D. H. Hoorn, A. Nzama, Bruce Merry, L. Sofeya, Sharmila Goedhart, L. R. S. Brederode, M. J. Hlakola, I. Rammala, O. Toruvanda, S. Rakoma, B. L. Fanaroff, A. Rust, A. Martens, M. G. Welz, Y. Padayachee, C. T. G. Schollar, S. J. Marais, B. Xaia, J. P. van Staden, F. Karels, T. Baloyi, B. de Swardt, I. Liebenberg, Vanessa A. Moss, A. L. Walker, C.G. Van der Merwe, W. S. New, E. C. Knox-Davies, R. Millenaar, P. Prozesky, L. J. du Toit, O. J. Mokone, K. Madisa, G. Sethosa, Griffin Foster, T. L. Grobler, Tom Alberts, S. S. Passmoor, F. Joubert, A. A. Patel, D. Koch, Ramesh Karuppusamy, L. Richter, Kshitij Thorat, O. Mahgoub, Jason Manley, C. Sharpe, M. J. Slabber, P. L. van der Merwe, S. Fataar, G. B. Taylor, M. Rasivhaga, P. Sunnylall, MacCalvin Kariseb, Gyula I. G. Józsa, A. R. Foley, N. Marais, M. A. Dikgale, J. P. Burger, C. Olyn, S. Paula, A. J. Otto, S. Ratcliffe, B. Pholoholo, R. Renil, T. Macdonald, Justin L. Jonas, R. van Rooyen, P. Scholz, Oleg Smirnov, B. H. Wallace, Fernando Camilo, A. Peens-Hough, S. Lamoor, F. Obies, L. Marais, T. J. Steyn, M. T. O. Ockards, O. Jacobs, C. Mjikelo, A. J. Tiplady, Roy Booth, D. Liebenberg, R. Strong, T. J. van Balla, P. C. van Niekerk, S. D. Matshawule, V. Van Tonder, C. de Waal, S. K. Sirothia, D. Rosekrans, R. M. Adam, L. Mafhungo, Matthew Bailes, G. Adams, P. P. A. Kotzé, D. M. Horn, S. Salie, M. S. de Villiers, Howard C. Reader, A. R. Isaacson, Dehann Fourie, B. Taljaard, C. de Villiers, A. F. Joubert, M. Serylak, T. Mauch, N. Sambu, Victoria M. Kaspi, C. C. Julius, N. Mnyandu, S. Seranyane, A. Krebs, Simon Johnston, N. Young, L. van den Heever, M. Manzini, R. van Wyk, M. Obrocka, N. Songqumase, T. W. Kusel, M. C. Mphego, J. A. Malan, I. P. T. Moeng, P. Malgas, K. J. Ngoasheng, B. M. Lunsky, L. C. Schwardt, M. Merryfield, W. van Straten, V. Thondikulam, B. Hugo, Nadeem Oozeer, Robert F. Archibald, P. Macfarlane, T. Cheetham, Aris Karastergiou, J. Conradie, D. Steyn, S. C. Gumede, S. Makhathini, S. W. P. Esterhuyse, N. Mkhabela, D. Booisen, R. P. M. Julie, Gianni Bernardi, L. Boyana, N. Kriek, Dirk I. L. de Villiers, T. Baxana, Cyril Tasse, M. Maree, Robert Lehmensiek, R. R. G. Gamatham, S. Zitha, D. E. Baker, K. Montshiwa, C. Magozore, Z. R. Ramudzuli, T. Gatsi, George Hobbs, S. J. Buchner, I. P. Theron, R. Siebrits, John Reynolds, A. Hokwana, F. Kapp, L. G. Magnus, V. A. Kasper, J. P. L. Main, J. van Aardt, David B. Davidson, ZAF, Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Galaxies, Etoiles, Physique, Instrumentation (GEPI), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), and PSL Research University (PSL)-PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Swift, individual (PSR J16224950) [pulsars], 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Magnetosphere, Flux, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Ephemeris, Magnetar, 01 natural sciences, general [pulsars], stars: neutron, stars: magnetars, neutron [stars], Pulsar, pulsars: general, 0103 physical sciences, magnetars [stars], 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, computer.programming_language, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Quiescent state, Astronomy and Astrophysics, Neutron star, pulsars: individual, Space and Planetary Science, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], computer
Abstract: New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and NuSTAR) observations of PSR J1622-4950 indicate that the magnetar, in a quiescent state since at least early 2015, reactivated between 2017 March 19 and April 5. The radio flux density, while variable, is approximately 100x larger than during its dormant state. The X-ray flux one month after reactivation was at least 800x larger than during quiescence, and has been decaying exponentially on a 111+/-19 day timescale. This high-flux state, together with a radio-derived rotational ephemeris, enabled for the first time the detection of X-ray pulsations for this magnetar. At 5%, the 0.3-6 keV pulsed fraction is comparable to the smallest observed for magnetars. The overall pulsar geometry inferred from polarized radio emission appears to be broadly consistent with that determined 6-8 years earlier. However, rotating vector model fits suggest that we are now seeing radio emission from a different location in the magnetosphere than previously. This indicates a novel way in which radio emission from magnetars can differ from that of ordinary pulsars. The torque on the neutron star is varying rapidly and unsteadily, as is common for magnetars following outburst, having changed by a factor of 7 within six months of reactivation., Comment: Published in ApJ (2018 April 5); 13 pages, 4 figures
Published: 2018

58. Improved 21 cm Epoch Of Reionization Power Spectrum Measurements with a Hybrid Foreground Subtraction and Avoidance Technique

Author: Jonathan C. Pober, Aaron R. Parsons, Nichole Barry, Wenyang Li, Adrian Liu, Carina Cheng, Matthew Kolopanis, Ian Sullivan, James E. Aguirre, Joshua S. Dillon, Gianni Bernardi, Saul A. Kohn, Richard F. Bradley, Daniel C. Jacobs, Joshua Kerrigan, David DeBoer, Adam Lanman, Adam P. Beardsley, Chris Carilli, Zaki S. Ali, and USA
Subjects: Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010308 nuclear & particles physics, Subtraction, Astrophysics::Instrumentation and Methods for Astrophysics, Spectral density, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Space and Planetary Science, Computer Science::Computer Vision and Pattern Recognition, 0103 physical sciences, Dark Ages, Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, Reionization, Instrumentation and Methods for Astrophysics (astro-ph.IM), Astrophysics::Galaxy Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Observations of the 21cm Epoch of Reionization (EoR) signal are dominated by Galactic and extragalactic foregrounds. The need for foreground removal has led to the development of two main techniques, often referred to as "foreground avoidance" and "foreground subtraction." Avoidance is associated with filtering foregrounds in Fourier space, while subtraction uses an explicit foreground model that is removed. Using 1088 hours of data from the 64-element PAPER array, we demonstrate that subtraction of a foreground model prior to delay-space foreground filtering results in a modest but measurable improvement of the performance of the filter. This proof-of-concept result shows that improvement stems from the reduced dynamic range requirements needed for the foreground filter: subtraction of a foreground model reduces the total foreground power, so for a fixed dynamic range, the filter can push towards fainter limits. We also find that the choice of window function used in the foreground filter can have an appreciable affect on the performance near the edges of the observing band. We demonstrate these effects using a smaller 3 hour sampling of data from the MWA, and find that the hybrid filtering and subtraction removal approach provides similar improvements across the band as seen in the case with PAPER-64., Comment: 20 pages, 12 figures
Published: 2018
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59. Advanced Diagnostics for the Study of Linearly Polarized Emission. II. Application to Diffuse Interstellar Radio Synchrotron Emission

Author: Bryan Gaensler, Geraint F. Lewis, Gianni Bernardi, Blakesley Burkhart, Michael Kesteven, Lister Staveley-Smith, Marijke Haverkorn, Sergio Poppi, E. Carretti, Naomi McClure-Griffiths, C. A. Herron, GBR, and AUS
Subjects: 010504 meteorology & atmospheric sciences, Astronomy, FOS: Physical sciences, Magnetohydrodynamic turbulence, 01 natural sciences, law.invention, Physics::Fluid Dynamics, law, 0103 physical sciences, Faraday cage, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Physics, Turbulence, Linear polarization, Astronomy and Astrophysics, Polarization (waves), Astrophysics - Astrophysics of Galaxies, Synchrotron, 3. Good health, Computational physics, Magnetic field, Interstellar medium, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: Diagnostics of polarized emission provide us with valuable information on the Galactic magnetic field and the state of turbulence in the interstellar medium, which cannot be obtained from synchrotron intensity alone. In Paper I (Herron et al. 2017b), we derived polarization diagnostics that are rotationally and translationally invariant in the $Q$-$U$ plane, similar to the polarization gradient. In this paper, we apply these diagnostics to simulations of ideal magnetohydrodynamic turbulence that have a range of sonic and Alfv\'enic Mach numbers. We generate synthetic images of Stokes $Q$ and $U$ for these simulations, for the cases where the turbulence is illuminated from behind by uniform polarized emission, and where the polarized emission originates from within the turbulent volume. From these simulated images we calculate the polarization diagnostics derived in Paper I, for different lines of sight relative to the mean magnetic field, and for a range of frequencies. For all of our simulations, we find that the polarization gradient is very similar to the generalized polarization gradient, and that both trace spatial variations in the magnetoionic medium for the case where emission originates within the turbulent volume, provided that the medium is not supersonic. We propose a method for distinguishing the cases of emission coming from behind or within a turbulent, Faraday rotating medium, and a method to partly map the rotation measure of the observed region. We also speculate on statistics of these diagnostics that may allow us to constrain the physical properties of an observed turbulent region., Comment: 34 pages, 25 figures, accepted for publication in ApJ
Published: 2018

60. Design and characterization of the Large-aperture Experiment to Detect the Dark Age (LEDA) radiometer systems

Author: Anastasia Fialkov, J. M. Hartman, J. Craig, T. Joseph W. Lazio, David MacMahon, G. B. Taylor, Lincoln J. Greenhill, Robert Kimberk, H. Garsden, Stephen Bourke, Frank K. Schinzel, Matthew R. Dexter, B. R. Barsdell, Gregg Hallinan, Steven W. Ellingson, Ryan M. Monroe, Jayce Dowell, Danny C. Price, Gianni Bernardi, Edward Tong, S. Leiker, Michael Eastwood, Marin M. Anderson, David P. Woody, Tarraneh Eftekhari, Jonathon Kocz, Dan Werthimer, USA, and Apollo - University of Cambridge Repository
Subjects: Physics, Radiometer, Spectral signature, instrumentation: detectors, 010308 nuclear & particles physics, Cosmic microwave background, FOS: Physical sciences, telescopes, Astronomy and Astrophysics, Owens Valley Radio Observatory, 01 natural sciences, Starlight, Interferometry, Space and Planetary Science, cosmology: observations, 0103 physical sciences, dark ages, reionization, first stars, Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, Reionization, computer, Instrumentation and Methods for Astrophysics (astro-ph.IM), Leda, Remote sensing, computer.programming_language
Abstract: The Large-Aperture Experiment to Detect the Dark Age (LEDA) was designed to detect the predicted O(100)mK sky-averaged absorption of the Cosmic Microwave Background by Hydrogen in the neutral pre- and intergalactic medium just after the cosmological Dark Age. The spectral signature would be associated with emergence of a diffuse Ly$\alpha$ background from starlight during 'Cosmic Dawn'. Recently, Bowman et al. (2018) have reported detection of this predicted absorption feature, with an unexpectedly large amplitude of 530 mK, centered at 78 MHz. Verification of this result by an independent experiment, such as LEDA, is pressing. In this paper, we detail design and characterization of the LEDA radiometer systems, and a first-generation pipeline that instantiates a signal path model. Sited at the Owens Valley Radio Observatory Long Wavelength Array, LEDA systems include the station correlator, five well-separated redundant dual polarization radiometers and backend electronics. The radiometers deliver a 30-85MHz band (16, Comment: Accepted to MNRAS
Published: 2018

61. Simulations of Galactic polarized synchrotron emission for Epoch of Reionization observations

Author: Gianni Bernardi, Mario G. Santos, and Marta Spinelli
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, law.invention, law, 0103 physical sciences, Faraday cage, 010303 astronomy & astrophysics, Reionization, Astrophysics::Galaxy Astrophysics, media_common, Leakage (electronics), Physics, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Polarization (waves), Redshift, Interstellar medium, Space and Planetary Science, Sky, Dark Ages, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The detection of the redshifted cosmological $21$~cm line signal requires the removal of the Galactic and extragalactic foreground emission, which is orders of magnitude brighter anywhere in the sky. Foreground cleaning methods currently used are efficient in removing spectrally smooth components. However, they struggle in the presence of not spectrally smooth contamination that is, therefore, potentially the most dangerous one. An example of this is the polarized synchrotron emission, which is Faraday rotated by the interstellar medium and leaks into total intensity due to instrumental imperfections. In this work we present new full-sky simulations of this polarized synchrotron emission in the $50-200$~MHz range, obtained from the observed properties of diffuse polarized emission at low frequencies. The simulated polarized maps are made publicly available, aiming to provide more realistic templates to simulate the effect of instrumental leakage and the effectiveness of foreground separation techniques., Comment: 9 pages, 11 figures
Published: 2018
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62. Erratum: 'PAPER-64 Constraints on Reionization: The 21 cm Power Spectrum at z = 8.4' (2015, ApJ, 809, 61)

Author: James E. Aguirre, William P. Walbrugh, Richard F. Bradley, David F. Moore, Irina I. Stefan, David DeBoer, Matthys Maree, David MacMahon, Adrian Liu, Jasper Horrell, Andre Walker, Aaron R. Parsons, Haoxuan Zheng, Matthew R. Dexter, Pat Klima, Gianni Bernardi, Jonathan C. Pober, Jasper Grobbelaar, Nima Razavi, Daniel C. Jacobs, Zaki S. Ali, Carina Cheng, Chris Carilli, USA, and ZAF
Subjects: Physics, 010308 nuclear & particles physics, Covariance matrix, Molecular, Spectral density, Estimator, Astronomy and Astrophysics, Context (language use), Astronomy & Astrophysics, Covariance, Atomic, 01 natural sciences, Weighting, Particle and Plasma Physics, Space and Planetary Science, 0103 physical sciences, Applied mathematics, Oversampling, Nuclear, 010303 astronomy & astrophysics, Astronomical and Space Sciences, Bootstrapping (statistics), Physical Chemistry (incl. Structural)
Abstract: Author(s): Ali, ZS; Parsons, AR; Zheng, H; Pober, JC; Liu, A; Aguirre, JE; Bradley, RF; Bernardi, G; Carilli, CL; Cheng, C; Deboer, DR; Dexter, MR; Grobbelaar, J; Horrell, J; Jacobs, DC; Klima, P; Macmahon, DHE; Maree, M; Moore, DF; Razavi, N; Stefan, II; Walbrugh, WP; Walker, A | Abstract: In this erratum, we retract the upper limits on the 21 cm power spectrum presented in the published article. The published article reported an upper limit on δ 212(k ) of (22.4 mK)2 at z= 8.4 in the range 0.15 l k l 0.5h Mpc-1. This analysis underestimated the level of signal loss, or attenuation of the target cosmological 21 cm signal associated with the chosen power spectrum estimator, and also underestimated the statistical error on those estimates. A revised result, with a new analysis, is presented in M. K. Kolopanis et al. (2018, in preparation). Below, we briefly summarize the errors in the original analysis and how they are corrected. For an indepth analysis and discussion of the errors, we refer the reader to Cheng et al. (2018). Signal loss was expected in the original analysis because the covariance matrices, C, used to weight the un-normalized bandpower estimates, qa, in (Formula Presented) were empirically estimated from a time-averaged finite ensemble of the data, x, such that (Formula Presented). While the true covariance C leads to an inherently unbiased lossless estimator of the power spectrum, using an empirically estimated Ĉ can lead to signal loss. Specifically, weighting data by an empirically estimated covariance carries the risk of overfitting and downweighting EoR fluctuations that are coupled to the data. In Cheng et al. (2018), it is shown that these couplings are especially strong in the fringe-rate filtered PAPER-64 data set. The first and most impactful error relates to the method by which signal loss was estimated. To assess signal loss from the empirically estimated covariance matrix, different realizations of mock cosmological signals e of known amplitudes are added to the original data to form a new data vector, (Formula Presented). New covariance matrices, (Formula Presented) are used to estimate un-normalized bandpowers (Formula Presented), which can be written as (Formula Presented). The normalized power estimate can then be compared to the known injected power in e to estimate signal loss. The key error in the previous analysis was to assume that, since e was statistically independent of x, that the two middle crossterms in Equation (2) would average to zero in an ensemble. However, as shown in Cheng et al. (2018) and Switzer et al. (2015), these cross-terms can contain significant negative power because Ĉr contains information that correlates the two vectors. Ignoring these cross-terms leads to a significant underestimate of signal loss. As a result, we presented negligible signal loss in our original analysis, when in fact approximately 99.99% of the signal was removed (Cheng et al. 2018). Correcting for the actual signal loss is the biggest factor revising the upper limit on 21 D2 . The second mistake made in the original analysis was to underestimate the statistical errors in the reported power spectrum estimates. The original analysis used a bootstrap resampling technique on power spectral measurements over the baseline and time axes. However, fringe-rate filtering introduces significant correlations in the data along the time axis. As is discussed in Cheng et al. (2018), bootstrapping across correlated samples can result in a significant underestimate of the variation in the data if the number of resamplings is not equal to the number of independent samples in the data, as in the case of the original analysis. The error bars associated with this oversampling were underestimated by approximately a factor of 2 (in mK). The revised analysis in M. K. Kolopanis et al. (2018, in preparation) only applies bootstrap resampling across the baseline axis to avoid this problem. The mistake in estimating the statistical errors should have become apparent when comparing results to our theoretical thermal noise sensitivity. Unfortunately, a third miscalculation was made in estimating the thermal noise sensitivity. As detailed in Cheng et al. (2018), this miscalculation stemmed from numerous small mismatches between the idealized analysis pipeline used to estimate sensitivity and the actual analysis applied to the data. As a result, our estimated thermal noise sensitivity was approximately a factor of 3 low (in mK), leading to the mistaken impression that our error bars were consistent with the level of thermal noise. In summary, we retract the power spectrum results shown in Figures 18 and 20 in the published article. Results that relied on the original limits, including those presented in Figure 21, are retracted. Additionally, the companion paper to the original manuscript, Pober et al. (2015), used the original limits to place constraints on the spin temperature of the intergalactic medium (IGM) at z=8.4. Our revised limits do not place significant constraints on the IGM temperature, and the results of Figure 4 from Pober et al. (2015) should be disregarded. However, we note that their analysis would still be relevant should a future experiment place constraints on the 21 cm signal similar to those claimed in the published article. An updated analysis of this same data set is presented in M. K. Kolopanis et al. (2018, in preparation), where these revised results are put into context with measurements at other redshifts.
Published: 2018

63. Polarized redundant-baseline calibration for 21 cm cosmology without adding spectral structure

Author: Saul A. Kohn, Nicholas S. Kern, Joshua S. Dillon, Chuneeta D. Nunhokee, Jonathan C. Pober, Aaron R. Parsons, Zaki S. Ali, Adrian Liu, Wenyang Li, Gianni Bernardi, James E. Aguirre, and USA
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Calibration (statistics), media_common.quotation_subject, first stars, interferometers [instrumentation], Degrees of freedom (statistics), FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astronomy & Astrophysics, 01 natural sciences, Cosmology, 0103 physical sciences, dark ages, reionization, first stars, dark ages, 010303 astronomy & astrophysics, Reionization, Instrumentation and Methods for Astrophysics (astro-ph.IM), media_common, Physics, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Universe, Computational physics, Interferometry, Space and Planetary Science, Sky, reionization, Degeneracy (mathematics), Astrophysics - Instrumentation and Methods for Astrophysics, Astronomical and Space Sciences, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: 21 cm cosmology is a promising new probe of the evolution of visible matter in our universe, especially during the poorly-constrained Cosmic Dawn and Epoch of Reionization. However, in order to separate the 21 cm signal from bright astrophysical foregrounds, we need an exquisite understanding of our telescopes so as to avoid adding spectral structure to spectrally-smooth foregrounds. One powerful calibration method relies on repeated simultaneous measurements of the same interferometric baseline to solve for the sky signal and for instrumental parameters simultaneously. However, certain degrees of freedom are not constrained by asserting internal consistency between redundant measurements. In this paper, we review the origin of these "degeneracies" of redundant-baseline calibration and demonstrate how they can source unwanted spectral structure in our measurement and show how to eliminate that additional, artificial structure. We also generalize redundant calibration to dual-polarization instruments, derive the degeneracy structure, and explore the unique challenges to calibration and preserving spectral smoothness presented by a polarized measurement., Comment: 12 pages, 3 figures, updated to match the published MNRAS version
Published: 2018

64. Measuring the global 21-cm signal with the MWA-I: improved measurements of the Galactic synchrotron background using lunar occultation

Author: Rachel L. Webster, Steven Tingay, Marcin Sokolowski, Gianni Bernardi, Benjamin McKinley, Natasha Hurley-Walker, Emil Lenc, J. L. B. Line, Randall B. Wayth, Cathryn M. Trott, A. R. Offringa, B. Pindor, F. Briggs, Judd D. Bowman, Christopher H. Jordan, Astronomy, ITA, USA, and AUS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010504 meteorology & atmospheric sciences, media_common.quotation_subject, first stars, SPECTRAL INDEX, FOS: Physical sciences, Murchison Widefield Array, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Occultation, 10 MHZ, law.invention, Telescope, SARAS, law, 0103 physical sciences, Astronomical interferometer, dark ages, reionization, first stars, dark ages, Moon, 010303 astronomy & astrophysics, Reionization, Instrumentation and Methods for Astrophysics (astro-ph.IM), 0105 earth and related environmental sciences, media_common, EPOCH, Physics, Spectral index, IONOSPHERE, Astrophysics::Instrumentation and Methods for Astrophysics, CONSTRAINTS, Astronomy, Astronomy and Astrophysics, RADAR DETERMINATION, MODEL, techniques: interferometric, Space and Planetary Science, Sky, Brightness temperature, RADIO-EMISSION, Physics::Space Physics, reionization, RADIATION, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present early results from a project to measure the sky-averaged (global), redshifted $21\,$cm signal from the Epoch of Reionisation (EoR), using the Murchison Widefield Array (MWA) telescope. Because interferometers are not sensitive to a spatially-invariant global average, they cannot be used to detect this signal using standard techniques. However, lunar occultation of the radio sky imprints a spatial structure on the global signal, allowing us to measure the average brightness temperature of the patch of sky immediately surrounding the Moon. In this paper we present one night of Moon observations with the MWA between 72 - 230 MHz and verify our techniques to extract the background sky temperature from measurements of the Moon's flux density. We improve upon previous work using the lunar occultation technique by using a more sophisticated model for reflected `earthshine' and by employing image differencing to remove imaging artefacts. We leave the Moon's (constant) radio brightness temperature as a free parameter in our fit to the data and as a result, measure $T_{\rm{moon}} = 180 \pm 12 $ K and a Galactic synchrotron spectral index of $-2.64\pm0.14$, at the position of the Moon. Finally, we evaluate the prospects of the lunar occultation technique for a global EoR detection and map out a way forward for future work with the MWA., Comment: 13 pages, 7 figures, accepted in MNRAS
Published: 2018
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65. A multifrequency radio continuum study of the Magellanic Clouds - I. Overall structure and star formation rates

Author: K. S. Srivani, Stephen M. Ord, Ravi Subrahmanyan, Pietro Procopio, Benjamin McKinley, Divya Oberoi, Luke Hindson, Andrew Williams, Thomas M. O. Franzen, John Morgan, Avinash A. Deshpande, Miroslav Filipovic, Thiagaraj Prabu, Stephen R. McWhirter, Chen Wu, Kevin Grieve, A. R. Offringa, Miguel F. Morales, Steven Tingay, Bi-Qing For, Anna D. Kapińska, Judd D. Bowman, Colin J. Lonsdale, Rachel L. Webster, Roger J. Cappallo, Eric R. Morgan, Paul Hancock, Christopher L. Williams, Joseph R. Callingham, Natasha Hurley-Walker, Emil Lenc, Lincoln J. Greenhill, Bryna J. Hazelton, Bryan Gaensler, Martin Bell, K. S. Dwarakanath, Daniel A. Mitchell, Lister Staveley-Smith, Melanie Johnston-Hollitt, Randall B. Wayth, N. Udaya Shankar, Qinghua Zheng, Gianni Bernardi, Jordan D. Collier, F. Briggs, David L. Kaplan, ITA, USA, and AUS
Subjects: Physics, 010308 nuclear & particles physics, media_common.quotation_subject, Library science, Astronomy and Astrophysics, Murchison Widefield Array, Astronomy & Astrophysics, 01 natural sciences, Space and Planetary Science, Excellence, Observatory, Research council, 0103 physical sciences, 010303 astronomy & astrophysics, media_common
Abstract: We present the first low-frequency Murchison Widefield Array (MWA) radio continuum maps of the Magellanic Clouds (MCs), using mosaics from the GaLactic Extragalactic All-Sky MWA (GLEAM) survey. In this paper, we discuss the overall radio continuum morphology between 76 and 227 MHz and compare them with neutral hydrogen maps, 1.4 GHz continuum maps and optical images. Variation of diffuse emission is noticeable across the Large Magellanic Cloud (LMC) but absent across the bar of the Small Magellanic Cloud (SMC). We also measure the integrated flux densities and derive the spectral indices for the MCs. A double power-law model with fixed α1 = -0.1 fit between 19.7 MHz and 8.55 GHz yields α0 = -0.66 ± 0.08 for the LMC. A power-law model yields α _{8.55 GHz}^{85.5 MHz} = -0.82± 0.03 for the SMC. The radio spectral index maps reveal distinctive flat and steep spectral indices for the H II regions and supernova remnants, respectively. We find strong correlation between H II regions and Hα emission. Using a new 150 MHz-Hα relation as a star formation rate indicator, we estimate global star formation rates of 0.068-0.161 M☉ yr-1 and 0.021-0.050 M☉ yr-1 for the LMC and SMC, respectively. Images in 20 frequency bands, and wideband averages are made available via the GLEAM virtual observatory server.
Published: 2018

66. Polarization leakage in epoch of reionization windows - I. Low Frequency Array observations of the 3C196 field

Author: Vishambhar Pandey, Abhik Ghosh, Emma Chapman, S. van der Tol, Saleem Zaroubi, Hannes Jensen, Harish Vedantham, Rajat M. Thomas, Ilian T. Iliev, A. G. de Bruyn, Vibor Jelić, O. Martinez-Rubi, K. M. B. Asad, F. B. Abdalla, Luitje Koopmans, Sarod Yatawatta, S. Daiboo, Gianni Bernardi, Garrelt Mellema, A. R. Offringa, Geraint Harker, Maaijke Mevius, Michiel A. Brentjens, Elizabeth Fernandez, Joop Schaye, B. Ciardi, A. H. Patil, S. Bus, ITA, GBR, FRA, DEU, NLD, Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], UMR Peuplement Végétaux et Bioagresseurs en Milieu Tropical (UMR PVBMT - INRA), Institut National de la Recherche Agronomique (INRA), Department of Physics and Astronomy [Ghent], Ghent University [Belgium] (UGENT), University College of London [London] (UCL), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, Netherlands Institute for Radio Astronomy (ASTRON), Max-Planck-Institut für Astrophysik (MPA), Max-Planck-Gesellschaft, Howard Hugues Medical Institute, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Department of Physics and Astronomy [UCL London], Department of Biochemistry and Microbiology, Plovdiv University 'Paisii Hilendarski, Stockholm University, AlbaNova University Center, Spatial Ecology and Epidemiology Group, University of Oxford [Oxford], Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Peuplements végétaux et bioagresseurs en milieu tropical (UMR PVBMT), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Université de La Réunion (UR), Universiteit Gent = Ghent University [Belgium] (UGENT), Howard Hughes Medical Institute (HHMI), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Universiteit Gent = Ghent University (UGENT), Harvard University-Smithsonian Institution, Plovdiv University 'Paisii Hilendarski', University of Oxford, Universiteit Leiden, Kapteyn Astronomical Institute, and Astronomy
Subjects: first stars, Field of view, polarization, instrumentation: polarimeters, intergalactic medium, cosmo-logy: observations, dark ages, reionization, Low frequency, 01 natural sciences, symbols.namesake, Optics, 0103 physical sciences, Stokes parameters, 010303 astronomy & astrophysics, Reionization, ComputingMilieux_MISCELLANEOUS, QB, Leakage (electronics), Physics, [PHYS]Physics [physics], 010308 nuclear & particles physics, business.industry, Spectral density, Astronomy and Astrophysics, LOFAR, Polarization (waves), Space and Planetary Science, symbols, business, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: Detection of the 21-cm signal coming from the epoch of reionization (EoR) is challenging especially because, even after removing the foregrounds, the residual Stokes I maps contain leakage from polarized emission that can mimic the signal. Here, we discuss the instrumental polarization of Low Frequency Array (LOFAR) and present realistic simulations of the leakages between Stokes parameters. From the LOFAR observations of polarized emission in the 3C196 field, we have quantified the level of polarization leakage caused by the nominal model beam of LOFAR, and compared it with the EoR signal using power spectrum analysis. We found that at 134-166 MHz, within the central 4° of the field the (Q, U) → I leakage power is lower than the EoR signal at k < 0.3 Mpc-1. The leakage was found to be localized around a Faraday depth of 0, and the rms of the leakage as a fraction of the rms of the polarized emission was shown to vary between 0.2 and 0.3 per cent, both of which could be utilized in the removal of leakage. Moreover, we could define an `EoR window' in terms of the polarization leakage in the cylindrical power spectrum above the point spread function (PSF)-induced wedge and below k∥ ̃ 0.5 Mpc-1, and the window extended up to k∥ ̃ 1 Mpc-1 at all k⊥ when 70 per cent of the leakage had been removed. These LOFAR results show that even a modest polarimetric calibration over a field of view of ≲ 4° in the future arrays like Square Kilometre Array will ensure that the polarization leakage remains well below the expected EoR signal at the scales of 0.02-1 Mpc-1.
Published: 2015

67. Power spectrum analysis of ionospheric fluctuations with the Murchison Widefield Array

Author: Martin Bell, Judd D. Bowman, Iver H. Cairns, Andrew Williams, Avinash A. Deshpande, N. Udaya Shankar, B. E. Corey, Steven Tingay, Alan E. E. Rogers, Gianni Bernardi, Lincoln J. Greenhill, R. Goeke, K. S. Srivani, Roger J. Cappallo, A. Roshi, E. Kratzenberg, Lu Feng, Stephen M. Ord, David L. Kaplan, A. R. Offringa, A. R. Whitney, David Emrich, Bryan Gaensler, T. Prabu, Paul Hancock, Shyeh Tjing Loi, Justin C. Kasper, Edward T. Morgan, Rachel L. Webster, Daniel A. Mitchell, Tara Murphy, Divya Oberoi, Frank H. Briggs, S. R. McWhirter, Mark Waterson, Nadia Kudryavtseva, John Morgan, Melanie Johnston-Hollitt, Bryna J. Hazelton, Colin J. Lonsdale, Randall B. Wayth, Christopher L. Williams, Mervyn J. Lynch, Ravi Subrahmanyan, Cathryn M. Trott, Miguel F. Morales, Natasha Hurley-Walker, and Emil Lenc
Subjects: Physics, Line-of-sight, 010504 meteorology & atmospheric sciences, Scattering, business.industry, Astrophysics::Instrumentation and Methods for Astrophysics, Spectral density, Murchison Widefield Array, Condensed Matter Physics, 01 natural sciences, Magnetic field, law.invention, Radio telescope, Optics, law, Physics::Space Physics, 0103 physical sciences, General Earth and Planetary Sciences, Electrical and Electronic Engineering, Ionosphere, Radar, business, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: Low-frequency, wide field-of-view (FoV) radio telescopes such as the Murchison Widefield Array (MWA) enable the ionosphere to be sampled at high spatial completeness. We present the results of the first power spectrum analysis of ionospheric fluctuations in MWA data, where we examined the position offsets of radio sources appearing in two datasets. The refractive shifts in the positions of celestial sources are proportional to spatial gradients in the electron column density transverse to the line of sight. These can be used to probe plasma structures and waves in the ionosphere. The regional (10-100 km) scales probed by the MWA, determined by the size of its FoV and the spatial density of radio sources (typically thousands in a single FoV), complement the global (100-1000 km) scales of GPS studies and local (0.01-1 km) scales of radar scattering measurements. Our data exhibit a range of complex structures and waves. Some fluctuations have the characteristics of travelling ionospheric disturbances (TIDs), while others take the form of narrow, slowly-drifting bands aligned along the Earth's magnetic field.
Published: 2015

68. Measuring phased-array antenna beampatterns with high dynamic range for the Murchison Widefield Array using 137 MHz ORBCOMM satellites

Author: D. L. Kaplan, N. Udaya Shankar, Frank H. Briggs, S. R. McWhirter, Melanie Johnston-Hollitt, Edward T. Morgan, Miguel F. Morales, Judd D. Bowman, Gianni Bernardi, T. Prabu, Randall B. Wayth, Stephen M. Ord, Rachel L. Webster, Christopher L. Williams, Andrew Williams, Steven Tingay, Colin J. Lonsdale, Avinash A. Deshpande, Lincoln J. Greenhill, Daniel A. Mitchell, Bryna J. Hazelton, R. Goeke, Abraham R. Neben, K. S. Srivani, Richard F. Bradley, Divya Oberoi, Ravi Subrahmanyan, Roger J. Cappallo, and Jacqueline N. Hewitt
Subjects: Physics, Beamforming, Main lobe, business.industry, Phased array, Astrophysics::Instrumentation and Methods for Astrophysics, 020206 networking & telecommunications, Murchison Widefield Array, 02 engineering and technology, Condensed Matter Physics, 01 natural sciences, law.invention, Optics, law, 0103 physical sciences, 0202 electrical engineering, electronic engineering, information engineering, Reference antenna, General Earth and Planetary Sciences, Dipole antenna, Electrical and Electronic Engineering, Antenna (radio), business, 010303 astronomy & astrophysics, High dynamic range
Abstract: Detection of the fluctuations in 21 cm line emission from neutral hydrogen during the Epoch of Reionization in thousand hour integrations poses stringent requirements on calibration and image quality, both of which necessitate accurate primary beam models. The Murchison Widefield Array (MWA) uses phased array antenna elements which maximize collecting area at the cost of complexity. To quantify their performance, we have developed a novel beam measurement system using the 137 MHz ORBCOMM satellite constellation and a reference dipole antenna. Using power ratio measurements, we measure the {\it in situ} beampattern of the MWA antenna tile relative to that of the reference antenna, canceling the variation of satellite flux or polarization with time. We employ angular averaging to mitigate multipath effects (ground scattering), and assess environmental systematics with a null experiment in which the MWA tile is replaced with a second reference dipole. We achieve beam measurements over 30 dB dynamic range in beam sensitivity over a large field of view (65\% of the visible sky), far wider and deeper than drift scans through astronomical sources allow. We verify an analytic model of the MWA tile at this frequency within a few percent statistical scatter within the full width at half maximum. Towards the edges of the main lobe and in the sidelobes, we measure tens of percent systematic deviations. We compare these errors with those expected from known beamforming errors.
Published: 2015

69. Real‐time imaging of density ducts between the plasmasphere and ionosphere

Author: Bryan Gaensler, Judd D. Bowman, Iver H. Cairns, Roger J. Cappallo, Edward T. Morgan, Colin J. Lonsdale, Randall B. Wayth, Cathryn M. Trott, Christopher L. Williams, Lu Feng, Miguel F. Morales, C. L. Waters, Ravi Subrahmanyan, Martin Bell, Lincoln J. Greenhill, Frederick W. Menk, Philip J. Erickson, Andrew Williams, N. Udaya Shankar, Stephen M. Ord, Natasha Hurley-Walker, Emil Lenc, Avinash A. Deshpande, Shyeh Tjing Loi, A. R. Offringa, Bryna J. Hazelton, Paul Hancock, Daniel A. Mitchell, Gianni Bernardi, Divya Oberoi, T. Prabu, Melanie Johnston-Hollitt, Steven Tingay, David L. Kaplan, Ronald D. Ekers, John Morgan, Frank H. Briggs, S. R. McWhirter, Rachel L. Webster, Tara Murphy, K. S. Srivani, ITA, USA, and AUS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP), Physics, FOS: Physical sciences, Magnetosphere, Murchison Widefield Array, Plasmasphere, Geophysics, Plasma, Space Physics (physics.space-ph), Physics::Geophysics, Magnetic field, Physics - Space Physics, Ionization, Electric field, Physics::Space Physics, General Earth and Planetary Sciences, Astrophysics::Earth and Planetary Astrophysics, Ionosphere, Astrophysics - Earth and Planetary Astrophysics
Abstract: Ionization of the Earth's atmosphere by sunlight forms a complex, multi-layered plasma environment within the Earth's magnetosphere, the innermost layers being the ionosphere and plasmasphere. The plasmasphere is believed to be embedded with cylindrical density structures (ducts) aligned along the Earth's magnetic field, but direct evidence for these remains scarce. Here we report the first direct wide-angle observation of an extensive array of field-aligned ducts bridging the upper ionosphere and inner plasmasphere, using a novel ground-based imaging technique. We establish their heights and motions by feature-tracking and parallax analysis. The structures are strikingly organized, appearing as regularly-spaced, alternating tubes of overdensities and underdensities strongly aligned with the Earth's magnetic field. These findings represent the first direct visual evidence for the existence of such structures., Accepted for publication in Geophysical Research Letters
Published: 2015

70. A digital-receiver for the MurchisonWidefield Array

Author: Mervyn J. Lynch, David L. Kaplan, N. Udaya Shankar, Grant Hampson, Judd D. Bowman, S. Madhavi, Lincoln J. Greenhill, R. Koenig, T. Booler, W. Arcus, Justin C. Kasper, D. Pallot, Gianni Bernardi, Stephen M. Ord, Ludi deSouza, Alan R. Whitney, Gopalakrishna M R, Eric Kratzenberg, Frank H. Briggs, Edward H. Morgan, John D. Bunton, Melanie Johnston-Hollitt, Stuart Wyithe, David Emrich, David Herne, Daniel A. Mitchell, Jamie Stevens, Joseph Pathikulangara, S. E. Tremblay, D. Anish Roshi, P. A. Kamini, Thiagaraj Prabu, B. B. Kincaid, Joseph E. Salah, K. S. Srivani, Brian Crosse, Randall B. Wayth, Brian E. Corey, Mark Waterson, Robert J. Sault, Ravi Subrahmanyan, Andrew Williams, Miguel F. Morales, Avinash A. Deshpande, Ronald A. Remillard, Rachel L. Webster, Divya Oberoi, Christopher L. Williams, Alan E. E. Rogers, Jacqueline N. Hewitt, Roger J. Cappallo, Robert F. Goeke, Steven Tingay, Deepak Kumar, David G. Barnes, Bryna J. Hazelton, Russell McWhirter, Colin J. Lonsdale, ITA, USA, AUS, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Goeke, Robert F., Morgan, Edward H., Williams, Christopher Leigh, Hewitt, Jacqueline N., Remillard, Ronald Alan, Kratzenberg, Eric W., McWhirter, Stephen R., Cappallo, Roger J., Corey, Brian E., Kincaid, Barton B., Lonsdale, Colin John, Oberoi, Divya, Rogers, Alan E. E., Salah, Joseph E., and Whitney, Alan R.
Subjects: Murchison meteorite, Optical fiber, business.industry, Computer science, Bandwidth (signal processing), FOS: Physical sciences, 020206 networking & telecommunications, Astronomy and Astrophysics, Murchison Widefield Array, 02 engineering and technology, Polarization (waves), 01 natural sciences, law.invention, Analog signal, Space and Planetary Science, Observatory, law, 0103 physical sciences, 0202 electrical engineering, electronic engineering, information engineering, Astrophysics - Instrumentation and Methods for Astrophysics, business, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Computer hardware
Abstract: An FPGA-based digital-receiver has been developed for a low-frequency imaging radio interferometer, the Murchison Widefield Array (MWA). The MWA, located at the Murchison Radio-astronomy Observatory (MRO) in Western Australia, consists of 128 dual-polarized aperture-array elements (tiles) operating between 80 and 300\,MHz, with a total processed bandwidth of 30.72 MHz for each polarization. Radio-frequency signals from the tiles are amplified and band limited using analog signal conditioning units; sampled and channelized by digital-receivers. The signals from eight tiles are processed by a single digital-receiver, thus requiring 16 digital-receivers for the MWA. The main function of the digital-receivers is to digitize the broad-band signals from each tile, channelize them to form the sky-band, and transport it through optical fibers to a centrally located correlator for further processing. The digital-receiver firmware also implements functions to measure the signal power, perform power equalization across the band, detect interference-like events, and invoke diagnostic modes. The digital-receiver is controlled by high-level programs running on a single-board-computer. This paper presents the digital-receiver design, implementation, current status, and plans for future enhancements., Comment: 14 pages, 7 figures
Published: 2015

71. Serendipitous discovery of a dying Giant Radio Galaxy associated with NGC 1534, using the Murchison Widefield Array

Author: Steven Tingay, Alan E. E. Rogers, Divya Oberoi, Roger J. Cappallo, Jacqueline N. Hewitt, A. Roshi, U. Shankar, Thiagaraj Prabu, David Emrich, Melanie Johnston-Hollitt, Russell McWhirter, Gianni Bernardi, K. S. Srivani, Richard W. Hunstead, Judd D. Bowman, Luke Hindson, David L. Kaplan, A. R. Offringa, Colin J. Lonsdale, Elaine M. Sadler, Mark Waterson, Stephen M. Ord, Bryna J. Hazelton, Miguel F. Morales, Edward H. Morgan, Bryan Gaensler, Frank H. Briggs, Christopher L. Williams, Rachel L. Webster, Justin C. Kasper, Randall B. Wayth, Ravi Subrahmanyan, Ron Ekers, Brian E. Corey, Paul Hancock, Daniel A. Mitchell, Alan R. Whitney, Mervyn J. Lynch, Andrew Williams, Avinash A. Deshpande, Lincoln J. Greenhill, Natasha Hurley-Walker, Eric Kratzenberg, Robert F. Goeke, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Rogers, Alan E. E., Whitney, Alan R., Hewitt, Jacqueline N., Morgan, Edward H., Williams, Christopher Leigh, ITA, USA, and AUS
Subjects: Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Murchison Widefield Array, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Luminosity, Hubble sequence, symbols.namesake, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Surface brightness, 010306 general physics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Luminous infrared galaxy, Physics, Astronomy, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies, Galaxy, Dust lane, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), symbols
Abstract: Recent observations with the Murchison Widefield Array at 185~MHz have serendipitously unveiled a heretofore unknown giant and relatively nearby ($z = 0.0178$) radio galaxy associated with NGC\,1534. The diffuse emission presented here is the first indication that NGC\,1534 is one of a rare class of objects (along with NGC\,5128 and NGC\,612) in which a galaxy with a prominent dust lane hosts radio emission on scales of $\sim$700\,kpc. We present details of the radio emission along with a detailed comparison with other radio galaxies with disks. NGC1534 is the lowest surface brightness radio galaxy known with an estimated scaled 1.4-GHz surface brightness of just 0.2\,mJy\,arcmin$^{-2}$. The radio lobes have one of the steepest spectral indices yet observed: $\alpha=-2.1\pm0.1$, and the core to lobe luminosity ratio is $, Comment: 12 pages, 7 figures, accepted MNRAS
Published: 2015

72. LOFAR discovery of a quiet emission mode in PSR B0823+26

Author: F. Breitling, Gottfried Mann, R. Pizzo, John D. Anderson, Cees Bassa, Sera Markoff, Rene P. Breton, Ashish Asgekar, Charlotte Sobey, E. Jütte, George Heald, Heino Falcke, P. Maat, M. J. Norden, M. A. Garrett, Jean-Mathias Grießmeier, Ph. Zarka, Rebecca McFadden, H. Paas, Ben Stappers, E. de Geus, Sarod Yatawatta, V. I. Kondratiev, D. D. Mulcahy, J. van Leeuwen, S. ter Veen, M. Pilia, M. Pandey-Pommier, Ralph A. M. J. Wijers, A. W. Gunst, J. Sluman, Olaf Wucknitz, H. J. A. Röttgering, Philip Best, Christian Vocks, D. McKay-Bukowski, Michel Tagger, D. Carbone, A. Alexov, Andrew Lyne, Antonia Rowlinson, A. Noutsos, Adam Stewart, Chiara Ferrari, T. E. Hassall, Evan Keane, Patrick Weltevrede, Jason W. T. Hessels, Satyendra Thoudam, S. Duscha, M. Serylak, A. van Duin, G. Pietka, Laura Birzan, Jochen Eislöffel, J. P. Hamaker, Wilfred Frieswijk, C. Toribio, Michael Kramer, D. A. Rafferty, A. G. Polatidis, Arthur Corstanje, A. Nelles, John D. Swinbank, Y. Tang, Anna M. M. Scaife, Martin Bell, N. J. Young, V. N. Pandey, Gerard H. Kuper, Cyril Tasse, J. W. Broderick, H. Munk, John McKean, Marcus Brüggen, Matthias Steinmetz, Annalisa Bonafede, A. Renting, Richard Fallows, R. Vermeulen, Mark J. Bentum, Matthias Hoeft, M. de Vos, Aris Karastergiou, Michael W. Wise, Gianni Bernardi, Jörg R. Hörandel, Rob Fender, Oleg Smirnov, Emanuela Orru, Dominik J. Schwarz, I. M. Avruch, Anna V. Bilous, R. J. van Weeren, Sobey, C., Young, N.J., Hessels, J.W.T., Weltevrede, P., Noutsos, A., Stappers, B.W., Kramer, M., Bassa, C., Lyne, A.G., Kondratiev V.I., null, Hassall, T.E., Keane, E.F., Bilous, A.V., Breton, R.P., Grießmeier, J.M., Karastergiou, A., Pilia, M., Serylak, M., Ter Veen, S., Van Leeuwen, J., Alexov, A., Anderson, J., Asgekar, A., Avruch, I.M., Bell, M.E., Bentum, M.J., Bernardi, G., Best, P., Bĭrzan, L., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Corstanje, A., Carbone, D., De Geus, E., De Vos, M., Van Duin, A., Duscha, S., Eislöffel, J., Falcke, H., Fallows, R.A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M.A., Gunst, A.W., Hamaker, J.P., Heald, G., Hoeft, M., Hörandel, J., Jütte, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., McKean, J.P., Mulcahy, D.D., Munk, H., Nelles, A., Norden, M.J., Orrù, E., Paas, H., Pandey-Pommier, M., Pandey, V.N., Pietka, G., Pizzo, R., Polatidis, A.G., Rafferty, D., Renting, A., Röttgering, H., Rowlinson, A., Scaife, A.M.M., Schwarz, D., Sluman, J., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Thoudam, S., Toribio, C., Vermeulen, R., Vocks, C., Van Weeren, R.J., Wijers, R.A.M.J., Wise, M.W., Wucknitz, O., Yatawatta, S., Zarka, P., Max-Planck-Institut für Radioastronomie (MPIFR), University of Minnesota [Twin Cities] (UMN), University of Minnesota System, University of Amsterdam [Amsterdam] (UvA), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Columbia Astrophysics Laboratory (CAL), Columbia University [New York], Cornell University [New York], Netherlands Institute for Radio Astronomy (ASTRON), Centre for Astrophysics and Supercomputing [Swinburne] (CAS), Swinburne University of Technology [Melbourne], Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University [Nijmegen], Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Rhodes University, Grahamstown, Oxford Astrophysics, University of Oxford, Institute for Mathematics Applied to Geoscience, National Center for Atmospheric Research [Boulder] (NCAR), SRON Netherlands Institute for Space Research (SRON), CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), University of Edinburgh, Leiden Observatory [Leiden], Universiteit Leiden, Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), University of Southampton, Medstar Research Institute, Thüringer Landessternwarte Tautenburg (TLS), Institute of Mathematical and Physical Sciences, Département de Géologie, Université de Montréal (UdeM), University Bochum, Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Oulu, Center for Information Technology CIT, Université de Groningen, Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), National Radio Astronomy Observatory [Charlottesville] (NRAO), National Radio Astronomy Observatory (NRAO), Department of Astronomy and Astrophysics [PennState], Pennsylvania State University (Penn State), Penn State System-Penn State System, School of Physics and Astronomy [Southampton], Interactions Son Musique Mouvement, Sciences et Technologies de la Musique et du Son (STMS), Institut de Recherche et Coordination Acoustique/Musique (IRCAM)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche et Coordination Acoustique/Musique (IRCAM)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), Laboratory for Atmospheric and Space Physics [Boulder] (LASP), University of Colorado [Boulder], Université Paris-Sud - Paris 11 (UP11), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), SKA South Africa, Ska South Africa, Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, We would like to thank R. Karuppusamy for his help with the Effelsberg observations. CF acknowledges financial support by the Agence Nationale de la Recherche through grant ANR-09-JCJC-0001-01., European Project: 337062,EC:FP7:ERC,ERC-2013-StG,DRAGNET(2014), ITA, GBR, FRA, DEU, NLD, Radboud university [Nijmegen], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO), University of Oxford [Oxford], Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Pierre et Marie Curie - Paris 6 (UPMC), Universiteit Leiden [Leiden], École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Harvard University [Cambridge]-Smithsonian Institution, Astronomy, and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: stars, PSR B0823+26-radio telescopes, Astronomy, Astrophysics::High Energy Astrophysical Phenomena, Pulsar planet, FOS: Physical sciences, neutron- pulsars, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, neutron [stars], Pulsar, Millisecond pulsar, Pulsars: individual: PSR B0823+26, individual, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, Astroparticle physics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, Stars: neutron, Stars, Neutron star, Astrophysics - Solar and Stellar Astrophysics, magnetosphere-pulsars, [SDU]Sciences of the Universe [physics], Space and Planetary Science, QUIET, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Astrophysics - High Energy Astrophysical Phenomena, individual: PSR B0823+26 [pulsars]
Abstract: PSR B0823+26, a 0.53-s radio pulsar, displays a host of emission phenomena over timescales of seconds to (at least) hours, including nulling, subpulse drifting, and mode-changing. Studying pulsars like PSR B0823+26 provides further insight into the relationship between these various emission phenomena and what they might teach us about pulsar magnetospheres. Here we report on the LOFAR discovery that PSR B0823+26 has a weak and sporadically emitting 'quiet' (Q) emission mode that is over 100 times weaker (on average) and has a nulling fraction forty-times greater than that of the more regularly-emitting 'bright' (B) mode. Previously, the pulsar has been undetected in the Q-mode, and was assumed to be nulling continuously. PSR B0823+26 shows a further decrease in average flux just before the transition into the B-mode, and perhaps truly turns off completely at these times. Furthermore, simultaneous observations taken with the LOFAR, Westerbork, Lovell, and Effelsberg telescopes between 110 MHz and 2.7 GHz demonstrate that the transition between the Q-mode and B-mode occurs within one single rotation of the neutron star, and that it is concurrent across the range of frequencies observed., Comment: 15 pages, 8 figures, 2 tables, accepted for publication in MNRAS
Published: 2015

73. Constraining Polarized Foregrounds for EOR Experiments II: Polarization Leakage Simulations in the Avoidance Scheme

Author: Nithyanandan Thyagarajan, Gianni Bernardi, James E. Aguirre, Aaron R. Parsons, T. L. Grobler, Chuneeta D. Nunhokee, Griffin Foster, J. Z. E. Martinot, Saul A. Kohn, Joshua S. Dillon, ITA, USA, and ZAF
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Population, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Spectral line, symbols.namesake, 0103 physical sciences, Faraday effect, education, 010303 astronomy & astrophysics, Reionization, Astrophysics::Galaxy Astrophysics, Physics, education.field_of_study, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Spectral density, Astronomy and Astrophysics, Polarization (waves), Redshift, Computational physics, Interstellar medium, Space and Planetary Science, symbols, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: A critical challenge in the observation of the redshifted 21-cm line is its separation from bright Galactic and extragalactic foregrounds. In particular, the instrumental leakage of polarized foregrounds, which undergo significant Faraday rotation as they propagate through the interstellar medium, may harmfully contaminate the 21-cm power spectrum. We develop a formalism to describe the leakage due to instrumental widefield effects in visibility-based power spectra measured with redundant arrays, extending the delay-spectrum approach presented in Parsons et al. (2012). We construct polarized sky models and propagate them through the instrument model to simulate realistic full-sky observations with the Precision Array to Probe the Epoch of Reionization. We find that the leakage due to a population of polarized point sources is expected to be higher than diffuse Galactic polarization at any $k$ mode for a 30~m reference baseline. For the same reference baseline, a foreground-free window at $k > 0.3 \, h$~Mpc$^{-1}$ can be defined in terms of leakage from diffuse Galactic polarization even under the most pessimistic assumptions. If measurements of polarized foreground power spectra or a model of polarized foregrounds are given, our method is able to predict the polarization leakage in actual 21-cm observations, potentially enabling its statistical subtraction from the measured 21-cm power spectrum., 11 pages, 10 figures, ApJ accepted
Published: 2017

74. Sardinia Radio Telescope observations of Abell 194. The intra-cluster magnetic field power spectrum

Author: Franco Vazza, Matteo Murgia, Gianni Bernardi, F. de Gasperin, Melanie Johnston-Hollitt, Raimondo Concu, Federica Govoni, M. Rossetti, Torsten A. Ensslin, Luigina Feretti, Tracy E. Clarke, Richard A. Perley, Rosita Paladino, Chiara Ferrari, M. Brienza, Marisa Girardi, G. B. Taylor, G. Giovannini, F. Gastaldello, H. Junklewitz, V. Vacca, W. Boschin, L. Gregorini, P. Parma, Sergio Poppi, Ettore Carretti, Emanuela Orrú, G. Valente, Annalisa Bonafede, S. Colafrancesco, Dominique Eckert, F. Loi, Andrea Melis, Astronomy, Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Govoni, F., Murgia, M., Vacca, V., Loi, F., Girardi, M., Gastaldello, F., Giovannini, G., Feretti, L., Paladino, R., Carretti, E., Concu, R., Melis, A., Poppi, S., Valente, G., Bernardi, G., Bonafede, A., Boschin, W., Brienza, M., Clarke, T. E., Colafrancesco, S., De Gasperin, F., Eckert, D., Enã lin, T. A., Ferrari, C., Gregorini, L., Johnston-Hollitt, M., Junklewitz, H., Orrã¹, E., Parma, P., Perley, R., Rossetti, M., B Taylor, G., Vazza, F., Joseph Louis LAGRANGE ( LAGRANGE ), Université Nice Sophia Antipolis ( UNS ), Université Côte d'Azur ( UCA ) -Université Côte d'Azur ( UCA ) -Observatoire de la Côte d'Azur, Université Côte d'Azur ( UCA ) -Centre National de la Recherche Scientifique ( CNRS ), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Enßlin, T. A., and Orrù, E.
Subjects: VELOCITY DISPERSIONS, Electron density, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Large-scale structure of Universe, Radio galaxy, [ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph], FOS: Physical sciences, REPRESENTATIVE SAMPLE, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, clusters: general [Galaxies], magnetic fields, 01 natural sciences, Power law, Radio telescope, 0103 physical sciences, FARADAY-ROTATION MAPS, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, galaxies: clusters: individual: Abell 194, VLA OBSERVATIONS, Physics, 010308 nuclear & particles physics, SCALE-INDEPENDENT METHOD, Spectral density, RICH CLUSTERS, Astronomy and Astrophysics, Astronomy and Astrophysic, Polarization (waves), Astrophysics - Astrophysics of Galaxies, clusters: individual: Abell 194 [Galaxies], Magnetic field, Space and Planetary Science, galaxies: clusters: general, Astrophysics of Galaxies (astro-ph.GA), ALL-SKY SURVEY, X-RAY, large-scale structure of Universe, HYDRA-A CLUSTER, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], GALAXY CLUSTERS, Galaxies: clusters: general, Galaxies: clusters: individual: Abell 194, Magnetic fields, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We study the intra-cluster magnetic field in the poor galaxy cluster Abell 194 by complementing radio data, at different frequencies, with data in the optical and X-ray bands. We analyze new total intensity and polarization observations of Abell 194 obtained with the Sardinia Radio Telescope (SRT). We use the SRT data in combination with archival Very Large Array observations to derive both the spectral aging and Rotation Measure (RM) images of the radio galaxies 3C40A and 3C40B embedded in Abell 194. The optical analysis indicates that Abell 194 does not show a major and recent cluster merger, but rather agrees with a scenario of accretion of small groups. Under the minimum energy assumption, the lifetimes of synchrotron electrons in 3C40B measured from the spectral break are found to be 157 Myrs. The break frequency image and the electron density profile inferred from the X-ray emission are used in combination with the RM data to constrain the intra-cluster magnetic field power spectrum. By assuming a Kolmogorov power law power spectrum, we find that the RM data in Abell 194 are well described by a magnetic field with a maximum scale of fluctuations of Lambda_max=64 kpc and a central magnetic field strength of =1.5 microG. Further out, the field decreases with the radius following the gas density to the power of eta=1.1. Comparing Abell 194 with a small sample of galaxy clusters, there is a hint of a trend between central electron densities and magnetic field strengths., Comment: Accepted by Astronomy and Astrophysics, 29 pages, 15 figures. Abstract abridged. A pdf version with high-quality figures can be downloaded from http://erg.oa-cagliari.inaf.it/preprints/a194_paper.pdf
Published: 2017

75. First limits on the 21 cm power spectrum during the Epoch of X-ray heating

Author: Thiagaraj Prabu, Lincoln J. Greenhill, Jonathan C. Pober, Stephen M. Ord, Andrei Mesinger, Eric Kratzenberg, Nichole Barry, Bartosz Pindor, Han-Seek Kim, Edward H. Morgan, J. L. B. Line, Christopher L. Williams, A. de Oliveira-Costa, Ian Sullivan, Benjamin McKinley, Joshua S. Dillon, David L. Kaplan, Andrew Williams, Daniel A. Mitchell, A. Roshi, N. Udaya Shankar, Cathryn M. Trott, Nithyanandan Thyagarajan, Rachel L. Webster, K. S. Srivani, J. Riding, Judd D. Bowman, Bryna J. Hazelton, Bryan Gaensler, A. R. Offringa, Miguel F. Morales, Lu Feng, Natasha Hurley-Walker, Pietro Procopio, Emil Lenc, Frank H. Briggs, Abraham R. Neben, Mark Waterson, Alan R. Whitney, Adam P. Beardsley, Gianni Bernardi, Chen Wu, Mervyn J. Lynch, Aaron Ewall-Wice, J. S. B. Wyithe, David Emrich, Brian E. Corey, P. Carroll, Justin C. Kasper, Max Tegmark, Shiv K. Sethi, Melanie Johnston-Hollitt, Divya Oberoi, Ravi Subrahmanyan, S. Paul, Randall B. Wayth, Abraham Loeb, Robert F. Goeke, Steven Tingay, Alan E. E. Rogers, Daniel C. Jacobs, Jacqueline N. Hewitt, Colin J. Lonsdale, Roger J. Cappallo, Stephen R. McWhirter, Massachusetts Institute of Technology. Department of Physics, MIT Kavli Institute for Astrophysics and Space Research, Ewall-Wice, Aaron Michael, Dillon, Joshua Shane, Hewitt, Jacqueline N, Neben, Abraham Richard, Tegmark, Max Erik, Feng, Lu, Goeke, Robert F, Astronomy, Ewall-Wice, A., Dillon, Joshua S., Hewitt, J. N., Loeb, A., Mesinger, A., Neben, A. R., Offringa, A. R., Tegmark, M., Barry, N., Beardsley, A. P., Bernardi, G., Bowman, Judd D., Briggs, F., Cappallo, R. J., Carroll, P., Corey, B. E., de Oliveira-Costa, A., Emrich, D., Feng, L., Gaensler, B. M., Goeke, R., Greenhill, L. J., Hazelton, B. J., Hurley-Walker, N., Johnston-Hollitt, M., Jacobs, Daniel C., Kaplan, D. L., Kasper, J. C., Kim, H, Kratzenberg, E., Lenc, E., Line, J., Lonsdale, C. J., Lynch, M. J., Mckinley, B., Mcwhirter, S. R., Mitchell, D. A., Morales, M. F., Morgan, E., Thyagarajan, Nithyanandan, Oberoi, D., Ord, S. M., Sourabh, Paul, Pindor, B., Pober, J. C., Prabu, T., Procopio, P., Riding, J., Rogers, A. E. E., Roshi, A., Shankar, N. Udaya, Sethi, Shiv K., Srivani, K. S., Subrahmanyan, R., Sullivan, I. S., Tingay, S. J., Trott, C. M., Waterson, M., Wayth, R. B., Webster, R. L., Whitney, A. R., Wu, C., Wyithe, J. S. B., Mesinger, ANDREI ALBERT, ITA, USA, and AUS
Subjects: dark age, Cosmology and Nongalactic Astrophysics (astro-ph.CO), media_common.quotation_subject, first stars, FOS: Physical sciences, Library science, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Settore FIS/05 - Astronomia e Astrofisica, Excellence, 0103 physical sciences, media_common.cataloged_instance, European union, IBM, dark ages, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Investment fund, media_common, Physics, Government, 010308 nuclear & particles physics, European research, first star, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, interferometric [techniques], galaxies [X-rays], X-rays: galaxies, 13. Climate action, Space and Planetary Science, techniques: interferometric, general [radio lines], Commonwealth, reionization, Christian ministry, Astrophysics - Instrumentation and Methods for Astrophysics, radio lines: general, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). 3 h of observations were conducted over two nights with significantly different levels of ionospheric activity. We use these data to assess the impact of systematic errors at low frequency, including the ionosphere and radio-frequency interference, on a power spectrum measurement. We find that after the 1–3 h of integration presented here, our measurements at the Murchison Radio Observatory are not limited by RFI, even within the FM band, and that the ionosphere does not appear to affect the level of power in the modes that we expect to be sensitive to cosmology. Power spectrum detections, inconsistent with noise, due to fine spectral structure imprinted on the foregrounds by reflections in the signal-chain, occupy the spatial Fourier modes where we would otherwise be most sensitive to the cosmological signal. We are able to reduce this contamination using calibration solutions derived from autocorrelations so that we achieve an sensitivity of 104 mK on comoving scales k ≲ 0.5 h Mpc[superscript −1]. This represents the first upper limits on the 21 cm power spectrum fluctuations at redshifts 12 ≲ z ≲ 18 but is still limited by calibration systematics. While calibration improvements may allow us to further remove this contamination, our results emphasize that future experiments should consider carefully the existence of and their ability to calibrate out any spectral structure within the EoR window., National Science Foundation (U.S.) (AST-0457585), National Science Foundation (U.S.) (AST-0821321), National Science Foundation (U.S.) (AST-1105835), National Science Foundation (U.S.) (AST-1410719), National Science Foundation (U.S.) (AST-1410484), National Science Foundation (U.S.) (AST-1411622), National Science Foundation (U.S.) (AST-1440343), National Science Foundation (U.S.) (1122374), National Science Foundation (U.S.) (PHY-0835713), National Science Foundation (U.S.) (CAREER-0847753), National Science Foundation (U.S.) (AST-0908884), United States. Air Force Office of Scientific Research (FA9550-0510247)
Published: 2017

76. A Matched Filter Technique For Slow Radio Transient Detection And First Demonstration With The Murchison Widefield Array

Author: Bryna J. Hazelton, Miguel F. Morales, Nadia Kudryavtseva, Paul Hancock, Ravi Subrahmanyan, Divya Oberoi, Bryan Gaensler, Andrew Williams, N. Udaya Shankar, Avinash A. Deshpande, Lincoln J. Greenhill, Steven Tingay, Rachel L. Webster, Christina L. Williams, K. S. Srivani, Edward H. Morgan, Colin J. Lonsdale, Tara Murphy, Ruslan Vaulin, Judd D. Bowman, Melanie Johnston-Hollitt, Gianni Bernardi, T. Prabu, Roger J. Cappallo, Lu Feng, Daniel A. Mitchell, Jacqueline N. Hewitt, Randall B. Wayth, Ronald A. Remillard, Stephen M. Ord, Frank H. Briggs, David L. Kaplan, S. R. McWhirter, ITA, USA, and AUS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010504 meteorology & atmospheric sciences, business.industry, Matched filter, media_common.quotation_subject, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Flux, Astronomy and Astrophysics, Murchison Widefield Array, 01 natural sciences, Optics, Space and Planetary Science, Sky, 0103 physical sciences, Limit (music), Transient (oscillation), Radio frequency, business, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Noise (radio), 0105 earth and related environmental sciences, media_common
Abstract: Many astronomical sources produce transient phenomena at radio frequencies, but the transient sky at low frequencies (, 16 pages, 14 figures, accepted to AJ
Published: 2017

77. MEQSILHOUETTE: a mm-VLBI observation and signal corruption simulator

Author: Oleg Smirnov, Roger Deane, Gianni Bernardi, Tariq Blecher, ITA, and ZAF
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Event Horizon Telescope, Supermassive black hole, 010504 meteorology & atmospheric sciences, Estimation theory, General relativity, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Silhouette, Interstellar medium, Space and Planetary Science, 0103 physical sciences, Very-long-baseline interferometry, Millimeter, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences
Abstract: The Event Horizon Telescope (EHT) aims to spatially resolve the silhouette (or shadow) of the supermassive black holes in the Galactic Centre (Sgr A$^\star$) and M87. The primary scientific objectives are to test general relativity in the strong-field regime and to probe accretion and jet-launch physics at event-horizon scales. This is made possible by the technique of Very Long Baseline Interferometry (VLBI) at (sub)millimetre wavelengths, which can achieve angular resolutions of order $\sim10~\mu$-arcsec. However, this approach suffers from unique observational challenges, including scattering in the troposphere and interstellar medium; rapidly time-variable source structure in both polarized and total intensity; as well as non-negligible antenna pointing errors. In this, the first paper in a series, we present the MeqSilhouette software package which is specifically designed to accurately simulate EHT observations. It includes realistic descriptions of a number of signal corruptions that can limit the ability to measure the key science parameters. This can be used to quantify calibration requirements, test parameter estimation and imaging strategies, and investigate systematic uncertainties that may be present. In doing so, a stronger link can be made between observational capabilities and theoretical predictions, with the goal of maximising scientific output from the upcoming order of magnitude increase in EHT sensitivity., Comment: Submitted to MNRAS, responded to first referee report. Comments are welcome
Published: 2017

78. A new perspective on turbulent Galactic magnetic fields through comparison of linear polarisation decomposition techniques

Author: E. Carretti, Bryan Gaensler, Jean-François Robitaille, Jason D. McEwen, M. J. Kesteven, M. Haverkorn, Gianni Bernardi, Sergio Poppi, Anna M. M. Scaife, Boris Leistedt, Lister Staveley-Smith, ITA, USA, and AUS
Subjects: Astronomy, FOS: Physical sciences, Superbubble, 01 natural sciences, 7. Clean energy, Image processing, Quantum mechanics, 0103 physical sciences, 010306 general physics, 010303 astronomy & astrophysics, ISM, Astrophysics::Galaxy Astrophysics, Physics, Linear polarization, Molecular cloud, Spherical harmonics, Astronomy and Astrophysics, Polarization (waves), Astrophysics - Astrophysics of Galaxies, Computational physics, Magnetic field, Radio continuum, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Polar, Energy source
Abstract: We compare two rotationally invariant decomposition techniques on linear polarisation data: the spin-2 spherical harmonic decomposition in two opposite parities, the $E$- and $B$-mode, and the multiscale analysis of the gradient of linear polarisation, $|\nabla \mathbf{P}|$. We demonstrate that both decompositions have similar properties in the image domain and the spatial frequency domain. They can be used as complementary tools for turbulence analysis of interstellar magnetic fields in order to develop a better understanding of the origin of energy sources for the turbulence, the origin of peculiar magnetic field structures and their underlying physics. We also introduce a new quantity $|\nabla EB|$ based on the $E$- and $B$-modes and we show that in the intermediate and small scales limit $|\nabla EB| \simeq |\nabla \mathbf{P}|$. Analysis of the 2.3 GHz S-band Polarization All Sky Survey (S -PASS) shows many extended coherent filament-like features appearing as 'double-jumps' in the $|\nabla \mathbf{P}|$ map that are correlated with negative and positive filaments of $B$-type polarisation. These local asymmetries between the two polarisation types, $E$ and $B$, of the non-thermal Galactic synchrotron emission have an influence on the $E$- and $B$-mode power spectra analyses. The wavelet-based formalism of the polarisation gradient analysis allows us to locate the position of $E$- or $B$-mode features responsible for the local asymmetries between the two polarisation types. In analysed subregions, the perturbations of the magnetic field are trigged by star clusters associated with HII regions, the Orion-Eridanus superbubble and the North Polar Spur at low Galactic latitude., Comment: Accepted for publication on MNRAS (2017 March 10), 20 pages, 14 figures
Published: 2017
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79. Spectral performance of SKA Log-periodic Antennas I: Mitigating spectral artefacts in SKA1-LOW 21-cm cosmology experiments

Author: Cathryn M. Trott, Andrew Faulkner, Jan Geralt bij de Vaate, Brett Wakley, Randall B. Wayth, Nicolas Fagnoni, Léon V. E. Koopmans, Eloy de Lera Acedo, Gianni Bernardi, ITA, GBR, AUS, NLD, Astronomy, De Lera Acedo, Eloy [0000-0001-8530-6989], and Apollo - University of Cambridge Repository
Subjects: LIMITATIONS, POWER SPECTRUM, Ripple, first stars, HYDROGEN EPOCH, FOS: Physical sciences, FOREGROUNDS, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, law.invention, Telescope, Optics, SCIENCE IMPLICATIONS, Observatory, law, 0103 physical sciences, dark ages, reionization, first stars, dark ages, 010303 astronomy & astrophysics, Reionization, Passband, Instrumentation and Methods for Astrophysics (astro-ph.IM), POLARIZATION LEAKAGE, Physics, CALIBRATION, 010308 nuclear & particles physics, business.industry, instrumentation: detectors, REIONIZATION ARRAY, Astrophysics::Instrumentation and Methods for Astrophysics, Spectral density, Astronomy and Astrophysics, SIMULATIONS, Amplitude, Space and Planetary Science, WINDOWS, reionization, Antenna (radio), Astrophysics - Instrumentation and Methods for Astrophysics, business
Abstract: This paper is the first in a series of papers describing the impact of antenna instrumental artefacts on the 21-cm cosmology experiments to be carried out by the low frequency instrument (SKA1-LOW) of the Square Kilometre Array telescope (SKA), i.e., the Cosmic Dawn (CD) and the Epoch of Reionization (EoR). The smoothness of the passband response of the current log-periodic antenna being developed for the SKA1-LOW is analyzed using numerical electromagnetic simulations. The amplitude variations over the frequency range are characterized using low-order polynomials defined locally, in order to study the impact of the passband smoothness in the instrument calibration and CD/EoR Science. A solution is offered to correct a fast ripple found at 60~MHz during a test campaign at the SKA site at the Murchison Radio-astronomy Observatory, Western Australia in September 2015 with a minor impact on the telescope's performance and design. A comparison with the Hydrogen Epoch of Reionization Array antenna is also shown demonstrating the potential use of the SKA1-LOW antenna for the Delay Spectrum technique to detect the EoR., Comment: 11 pages, 12 figures, accepted for publication (MNRAS)
Published: 2017
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80. The First Murchison Widefield Array low-frequency radio observations of cluster scale non-thermal emission: the case of Abell 3667

Author: Bryna J. Hazelton, Bryan Gaensler, Melanie Johnston-Hollitt, Thiagaraj Prabu, Martin Bell, Gianni Bernardi, Christopher L. Williams, Natasha Hurley-Walker, Emil Lenc, Bartosz Pindor, David L. Kaplan, Robert F. Goeke, A. Roshi, Daniel C. Jacobs, N. Udaya Shankar, K. S. Dwarakanath, Steven Tingay, Alan E. E. Rogers, David Emrich, Brian E. Corey, A. R. Offringa, Daniel A. Mitchell, Luke Hindson, Ettore Carretti, M. J. Lynch, N. D. R. Bhat, Lincoln J. Greenhill, Judd D. Bowman, J. Riding, Colin J. Lonsdale, Randall B. Wayth, Eric R. Morgan, Frank H. Briggs, Miguel F. Morales, Mark Waterson, Stephen M. Ord, Aaron Ewall-Wice, Benjamin McKinley, Alan R. Whitney, Justin C. Kasper, K. S. Srivani, Pietro Procopio, Divya Oberoi, Eric Kratzenberg, Andrew Williams, Avinash A. Deshpande, Roger J. Cappallo, John Morgan, K. Buckley, Rachel L. Webster, Nadia Kudryavtseva, Ravi Subrahmanyan, Stephen R. McWhirter, and Lu Feng
Subjects: Physics, FOS: Physical sciences, Astronomy, Astronomy and Astrophysics, Murchison Widefield Array, Astrophysics, Astrophysics - Astrophysics of Galaxies, 01 natural sciences, Galaxy, Radio relics, Radio halo, X-shaped radio galaxy, Abell 2744, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), 0103 physical sciences, Abell 520, 010306 general physics, 010303 astronomy & astrophysics, Galaxy cluster
Abstract: We present the first Murchison Widefield Array observations of the well-known cluster of galaxies Abell 3667 (A3667) between 105 and 241 MHz. A3667 is one of the best known examples of a galaxy cluster hosting a double radio relic and has been reported to contain a faint radio halo and bridge. The origins of radio halos, relics and bridges is still unclear, however galaxy cluster mergers seems to be an important factor. We clearly detect the North-West (NW) and South-East (SE) radio relics in A3667 and find an integrated flux density at 149 MHz of 28.1 +/- 1.7 and 2.4 +/- 0.1 Jy, respectively, with an average spectral index, between 120 and 1400 MHz, of -0.9 +/- 0.1 for both relics. We find evidence of a spatial variation in the spectral index across the NW relic steepening towards the centre of the cluster, which indicates an ageing electron population. These properties are consistent with higher frequency observations. We detect emission that could be associated with a radio halo and bridge. How- ever, due to the presence of poorly sampled large-scale Galactic emission and blended point sources we are unable to verify the exact nature of these features., 17 pages, 11 figures
Published: 2014

81. A close-pair binary in a distant triple supermassive black hole system

Author: Sándor Frey, Ian Heywood, K. J. B. Grainge, Rob Fender, Clare Rumsey, Roger Deane, Gianni Bernardi, Hans-Rainer Klöckner, Mickael Coriat, Matt J. Jarvis, and Zsolt Paragi
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Supermassive black hole, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Multidisciplinary, Sphere of influence (black hole), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astrophysics - Astrophysics of Galaxies, Black hole, General Relativity and Quantum Cosmology, Binary black hole, Intermediate-mass black hole, Astrophysics of Galaxies (astro-ph.GA), Stellar black hole, Spin-flip, Astrophysics - High Energy Astrophysical Phenomena, Schwarzschild radius, Astrophysics::Galaxy Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Galaxies are believed to evolve through merging, which should lead to multiple supermassive black holes in some. There are four known triple black hole systems, with the closest pair being 2.4 kiloparsecs apart (the third component is more distant at 3 kiloparsecs), which is far from the gravitational sphere of influence of a black hole with mass $\sim$10$^9$ M$_\odot$ (about 100 parsecs). Previous searches for compact black hole systems concluded that they were rare, with the tightest binary system having a separation of 7 parsecs. Here we report observations of a triple black hole system at redshift z=0.39, with the closest pair separated by $\sim$140 parsecs. The presence of the tight pair is imprinted onto the properties of the large-scale radio jets, as a rotationally-symmetric helical modulation, which provides a useful way to search for other tight pairs without needing extremely high resolution observations. As we found this tight pair after searching only six galaxies, we conclude that tight pairs are more common than hitherto believed, which is an important observational constraint for low-frequency gravitational wave experiments., 21 pages, 6 figures. Published online by Nature on 25 June 2014. Extremely minor differences with published version exist
Published: 2014

82. LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra

Author: Aris Karastergiou, Michael W. Wise, Gianni Bernardi, Heino Falcke, L. Cerrigone, D. Engels, Michel Tagger, Simona Vegetti, Anna Nelles, R. Morganti, John D. Swinbank, Leith Godfrey, George Heald, I. van Bemmel, E. Juette, P. Maat, Sera Markoff, V. I. Kondratiev, Léon V. E. Koopmans, Huib Intema, Adam Deller, H. Munk, J. W. Broderick, Marcus Brüggen, R. Blaauw, J. Sluman, M. Iacobelli, R. J. van Weeren, Roberto Pizzo, Philip Best, A. J. van der Horst, D. McKay-Bukowski, Wilfred Frieswijk, M. Pandey-Pommier, Martin J. Hardcastle, M. Pietka, Aleksandar Shulevski, Rainer Beck, Satyendra Thoudam, M. Serylak, Matthias Steinmetz, Anna M. M. Scaife, Emanuela Orrú, Antonia Rowlinson, D. D. Mulcahy, Sarod Yatawatta, H. Paas, Adam Stewart, S. Duscha, I. M. Avruch, Frank Breitling, B. Ciardi, John McKean, H. J. A. Röttgering, R. C. Vermeulen, Oleg Smirnov, Olaf Wucknitz, W. Reich, Gottfried Mann, F. de Gasperin, P. Zarka, M. Kuniyoshi, D. Rafferty, Martin Bell, Richard Fallows, James M. Anderson, G. Kuper, Mark J. Bentum, M. A. Garrett, J.-M. Grießmeier, Matthias Hoeft, Christian Vocks, M. P. van Haarlem, M. C. Toribio, A. G. Polatidis, J. van Leeuwen, Annalisa Bonafede, Rebecca McFadden, Netherlands Institute for Radio Astronomy (ASTRON), SRON Netherlands Institute for Space Research (SRON), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), University of Hertfordshire [Hatfield] (UH), Department of Astronomy and Astrophysics [PennState], Pennsylvania State University (Penn State), Penn State System-Penn State System, Department of Atmospheric and Planetary Sciences [Hampton] (APS), Hampton University, Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Université de Tours (UT), CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), University of Southampton, Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), University of Edinburgh, Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University [Nijmegen], Institute of Mathematical and Physical Sciences, Leiden Observatory [Leiden], Universiteit Leiden, Unité Scientifique de la Station de Nançay (USN), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Joint Institute for VLBI in Europe (JIVE ERIC), Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Ruhr-Universität Bochum [Bochum], Oxford Astrophysics, University of Oxford, Max-Planck-Institut für Radioastronomie (MPIFR), University of Oulu, University of Groningen, Groningen, Netherlands, Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Australia Telescope National Facility (ATNF), School of Physics and Astronomy [Southampton], Department of Physics and Astronomy [South Africa], University of the Western Cape (UWC), Rhodes University, Grahamstown, Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), Laboratory for Atmospheric and Space Physics [Boulder] (LASP), University of Colorado [Boulder], Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), European Project: 320745,EC:FP7:ERC,ERC-2012-ADG_20120216,RADIOLIFE(2013), Astronomy, McKean, J.P., Godfrey, L.E.H., Vegetti, S., Wise, M.W., Morganti, R., Hardcastle, M.J., Rafferty, D., Anderson, J., Avruch, I.M., Beck, R., Bell, M.E., van Bemmel, I., Bentum, M.J., Bernardi, G., Best, P., Blaauw, R., Bonafede, A., Breitling, F., Broderick, J.W., Brüggen, M., Cerrigone, L., Ciardi, B., de Gasperin, F., Deller, A., Duscha, S., Engels, D., Falcke, H., Fallows, R.A., Frieswijk, W., Garrett, M.A., Grießmeier, J.M., van Haarlem, M.P., Heald, G., Hoeft, M., van der HorstA.J., null, Iacobelli, M., Interna, H., Juette, E., Karastergiou, A., Kondratiev, V.I., Koopmans, L.V.E., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Mulcahy, D.D., Munk, H., Nelles, A., Orru, E., Paas, H., Pandey-Pommier, M., Pietka, M., Pizzo, R., Polatidis, A.G., Reich, W., Rottgering, H.J.A., Rowlinson, A., Scaife, A.M.M., Serylak, M., Shulevski, A., Sluman, J., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Thoudam, S., Toribio, M.C., Vermeulen, R., Vocks, C., van Weeren, R.J., Wucknitz, O., Yatawatta, S., Zarka, P., High Energy Astrophys. & Astropart. Phys (API, FNWI), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Pierre et Marie Curie - Paris 6 (UPMC), Radboud university [Nijmegen], Universiteit Leiden [Leiden], Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), University of Oxford [Oxford], École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), University of the Western Cape, Smithsonian Institution-Harvard University [Cambridge], ITA, GBR, FRA, DEU, NLD, Université de Tours, Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), and Harvard University [Cambridge]-Smithsonian Institution
Subjects: Radio galaxy, Astronomy, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Radio continuum: galaxie, Spectral line, Radio spectrum, Radio continuum: galaxies, Galaxies: active: individual: Cygnus A, X-shaped radio galaxy, 0103 physical sciences, Cygnus A, 010303 astronomy & astrophysics, Physics, Spectral index, EWI-27659, 010308 nuclear & particles physics, LOBES, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, Astrophysics - Astrophysics of Galaxies, Galaxy, galaxies [radio continuum], GALAXIES, METIS-321690, RESOLUTION, Space and Planetary Science, HOT-SPOTS, GAS, [SDU]Sciences of the Universe [physics], Astrophysics of Galaxies (astro-ph.GA), ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, ARRAY, IR-103274
Abstract: The low-frequency radio spectra of the hotspots within powerful radio galaxies can provide valuable information about the physical processes operating at the site of the jet termination. These processes are responsible for the dissipation of jet kinetic energy, particle acceleration, and magnetic-field generation. Here we report new observations of the powerful radio galaxy Cygnus A using the Low Frequency Array (LOFAR) between 109 and 183 MHz, at an angular resolution of ~3.5 arcsec. The radio emission of the lobes is found to have a complex spectral index distribution, with a spectral steepening found towards the centre of the source. For the first time, a turnover in the radio spectrum of the two main hotspots of Cygnus A has been directly observed. By combining our LOFAR imaging with data from the Very Large Array at higher frequencies, we show that the very rapid turnover in the hotspot spectra cannot be explained by a low-energy cut-off in the electron energy distribution, as has been previously suggested. Thermal (free-free) absorption or synchrotron self absorption models are able to describe the low-frequency spectral shape of the hotspots, however, as with previous studies, we find that the implied model parameters are unlikely, and interpreting the spectra of the hotspots remains problematic., Comment: 9 pages, 3 figures, accepted for publication in MNRAS
Published: 2016

83. Prospects for detecting the 21 cm forest from the diffuse intergalactic medium with LOFAR

Author: Vibor Jelić, Vishambhar Pandey, Gianni Bernardi, Garrelt Mellema, Sarod Yatawatta, S. Daiboo, P. Labropoulos, L. Graziani, V. Veligatla, James S. Bolton, Saleem Zaroubi, Antonella Maselli, Joop Schaye, Rajat M. Thomas, Geraint Harker, Harish Vedantham, B. Ciardi, Michiel A. Brentjens, A. R. Offringa, S. Kazemi, Luitje Koopmans, de Antonius Bruyn, O. Martinez, Astronomy, Kapteyn Astronomical Institute, Ciardi, B., Labropoulos, P., Maselli, A., Thomas Rajat, M., Zaroubi, S., Graziani, L., Bolton, J. S., Bernardi, G., Brentjens, M., de Bruyn, A. G., Daiboo, S., Harker, G. J. A., Jelic, V., Kazemi, S., Koopmans, L. V. E., Martinez, O., Mellema, G., Offringa, A. R., Pandey, V. N., Schaye, J., Veligatla, V., Vedantham, H., and Yatawatta, S.
Subjects: radio continuum: general, FOREGROUNDS, Astrophysics, general [Radio lines], 01 natural sciences, Spectral line, reionization: first star [Dark ages], RADIATIVE-TRANSFER, Radiative transfer, ABSORPTION, Radio astronomy, dark ages, Absorption (electromagnetic radiation), 010303 astronomy & astrophysics, Physics, general [Radio continuum], FLUCTUATIONS, CENTIMETER TOMOGRAPHY, reionization, intergalactic medium, radio lines: general, Astrophysics - Cosmology and Nongalactic Astrophysics, COSMIC REIONIZATION, Cosmology and Nongalactic Astrophysics (astro-ph.CO), first stars, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, radio astronomy, Dark ages: reionization: first stars, Radio telescope, Intergalactic medium, Radio continuum: general, Radio lines: general, LY-ALPHA, Settore FIS/05 - Astronomia e Astrofisica, 21-CM EMISSION, 0103 physical sciences, dark ages, reionization, first stars, Reionization, EPOCH, 010308 nuclear & particles physics, Astronomy, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, Redshift, 13. Climate action, Space and Planetary Science, Hydrogen line, HIGH-REDSHIFT
Abstract: We discuss the feasibility of the detection of the 21cm forest in the diffuse IGM with the radio telescope LOFAR. The optical depth to the 21cm line has been derived using simulations of reionization which include detailed radiative transfer of ionizing photons. We find that the spectra from reionization models with similar total comoving hydrogen ionizing emissivity but different frequency distribution look remarkably similar. Thus, unless the reionization histories are very different from each other (e.g. a predominance of UV vs. x-ray heating) we do not expect to distinguish them by means of observations of the 21cm forest. Because the presence of a strong x-ray background would make the detection of 21cm line absorption impossible, the lack of absorption could be used as a probe of the presence/intensity of the x-ray background and the thermal history of the universe. Along a random line of sight LOFAR could detect a global suppression of the spectrum from z>12, when the IGM is still mostly neutral and cold, in contrast with the more well-defined, albeit broad, absorption features visible at lower redshift. Sharp, strong absorption features associated with rare, high density pockets of gas could be detected also at z~7 along preferential lines of sight., 12 pages, 13 figures. MNRAS, in press
Published: 2013

84. Synchronous X-ray and Radio Mode Switches: A Rapid Global Transformation of the Pulsar Magnetosphere

Author: Y. Tang, Anna M. M. Scaife, Steve Rawlings, Aris Karastergiou, Michael W. Wise, Harvey Butcher, B. Ciardi, S. Duscha, V. N. Pandey, Gianni Bernardi, John McKean, Charlotte Sobey, Emanuela Orrú, Chiara Ferrari, M. Kuniyoshi, H. Munk, Marcus Brüggen, Michael Kramer, Cyril Tasse, J. W. Broderick, E. de Geus, Ashish Asgekar, Jason W. T. Hessels, F. de Gasperin, Matthias Hoeft, George Heald, L. Kuiper, A. P. Schoenmakers, P. Maat, R. H. van de Brink, Sera Markoff, Dipanjan Mitra, Philip Best, G. Wright, Ralph A. M. J. Wijers, J. de Plaa, Heino Falcke, V. I. Kondratiev, Rahul Basu, A. Noutsos, T. Coenen, Benjamin Stappers, Michel Tagger, Frank Breitling, Giulia Macario, Rob Fender, Rene C. Vermeulen, Michael R. Bell, F. Batejat, A. Alexov, Marco Iacobelli, H. Paas, Sarod Yatawatta, Patrick Weltevrede, Tim Hassall, R. J. van Weeren, W. Reich, M. Pilia, Laura Birzan, W. Hermsen, Evan Keane, Aleksandar Shulevski, Mark J. Bentum, M. Serylak, Martin Bell, Annalisa Bonafede, J. van Leeuwen, A. Horneffer, Jochen Eislöffel, Maaijke Mevius, H. J. A. Röttgering, A. G. Polatidis, R. Morganti, I. M. Avruch, S. ter Veen, A. W. Gunst, Olaf Wucknitz, Matthias Steinmetz, M. Pandey-Pommier, K. Zagkouris, J. Sluman, Roberto Pizzo, Jean-Mathias Grießmeier, G. Kuper, Philippe Zarka, Joanna M. Rankin, M. A. Garrett, James Miller-Jones, Wilfred Frieswijk, Hermsen, W., Hessels, J.W.T., Kuiper, L., Van Leeuwen, J., Mitra, D., De Plaa, J., Rankin, J.M., Stappers, B.W., Wright, G.A.E., Basu, R., Alexov, A., Coenen, T., Grießmeier, J.-M., Hassall, T.E., Karastergiou, A., Keane, E., Kondratiev, V.I., Kramer, M., Kuniyoshi, M., Noutsos, A., Serylak, M., Pilia, M., Sobey, C., Weltevrede, P., Zagkouris, K., Asgekar, A., Avruch, I.M., Batejat, F., Bell, M.E., Bell, M.R., Bentum, M.J., Bernardi, G., Best, P., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Butcher, H.R., Ciardi, B., Duscha, S., Eislöffel, J., Falcke, H., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M.A., De Gasperin, F., De Geus, E., Gunst, A.W., Heald, G., Hoeft, M., Horneffer, A., Iacobelli, M., Kuper, G., Maat, P., Macario, G., Markoff, S., McKean, J.P., Mevius, M., Miller-Jones, J.C.A., Morganti, R., Munk, H., Orrú, E., Paas, H., Pandey-Pommier, M., Pandey, V.N., Pizzo, R., Polatidis, A.G., Rawlings, S., Reich, W., Röttgering, H., Scaife, A.M.M., Schoenmakers, A., Shulevski, A., Sluman, J., Steinmetz, M., Tagger, M., Tang, Y., Tasse, C., Ter Veen, S., Vermeulen, R., Van De Brink, R.H., Van Weeren, R.J., Wijers, R.A.M.J., Wise, M.W., Wucknitz, O., Yatawatta, S., Zarka, P., SRON Netherlands Institute for Space Research (SRON), University of Amsterdam [Amsterdam] (UvA), National Centre for Radio Astrophysics [Pune] (NCRA), Tata Institute for Fundamental Research (TIFR), University of Vermont [Burlington], Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Astronomy Centre, University of Sussex, Space Telescope Science Institute (STSci), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Oxford Astrophysics, University of Oxford, Centre for Astrophysics and Supercomputing, Swinburne University of Technology [Melbourne], Netherlands Institute for Radio Astronomy (ASTRON), Max-Planck-Institut für Radioastronomie (MPIFR), Onsala Space Observatory (OSO), Chalmers University of Technology [Göteborg], University of Southampton, Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, University of Edinburgh, Leiden Observatory [Leiden], Universiteit Leiden, Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Thüringer Landessternwarte Tautenburg (TLS), Radboud University [Nijmegen], Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Medstar Research Institute, Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Center for Information Technology CIT, Université de Groningen, Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), National Radio Astronomy Observatory [Charlottesville] (NRAO), National Radio Astronomy Observatory (NRAO), School of Physics and Astronomy [Southampton], SKA South Africa, Ska South Africa, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, ANR-09-JCJC-0001,OPALES(2009), Kapteyn Astronomical Institute, Astronomy, Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), University of Oxford [Oxford], Harvard University [Cambridge]-Smithsonian Institution, Universiteit Leiden [Leiden], Radboud university [Nijmegen], Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: Electromagnetic field, POLARIZATION, Electromagnetic spectrum, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, FOS: Physical sciences, Magnetosphere, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, EMPIRICAL-THEORY, 01 natural sciences, Binary pulsar, Pulsar, Millisecond pulsar, 0103 physical sciences, 010306 general physics, XMM-NEWTON OBSERVATIONS, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, DRIFTING SUBPULSES, Multidisciplinary, B0943+10, Polarization (waves), GAMMA-RAY, [SDU]Sciences of the Universe [physics], 13. Climate action, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, RADIATION, EMISSION, Astrophysics - High Energy Astrophysical Phenomena, PHOTON IMAGING CAMERA, POWERED PULSARS, Radio wave
Abstract: Pulsars emit low-frequency radio waves through to high-energy gamma-rays that are generated anywhere from the surface out to the edges of the magnetosphere. Detecting correlated mode changes in the multi-wavelength emission is therefore key to understanding the physical relationship between these emission sites. Through simultaneous observations, we have detected synchronous switching in the radio and X-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio 'bright' mode, the X-rays show only an un-pulsed, non-thermal component. Conversely, when the pulsar is in a radio 'quiet' mode, the X-ray luminosity more than doubles and a 100%-pulsed thermal component is observed along with the non-thermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories., Paper published in Science including supplementary material
Published: 2013

85. Time-domain and spectral properties of pulsars at 154 MHz

Author: D. Oberoi, Daniel A. Mitchell, Thiagaraj Prabu, Colin J. Lonsdale, Joseph K. Swiggum, Steven Tingay, Paul Hancock, David L. Kaplan, Gianni Bernardi, Bryna J. Hazelton, Bryan Gaensler, Joseph R. Callingham, Melanie Johnston-Hollitt, E. Morgan, Christopher L. Williams, Miguel F. Morales, Natasha Hurley-Walker, Ravi Subrahmanyan, Antonia Rowlinson, Judd D. Bowman, Martin Bell, Stephen M. Ord, K. S. Srivani, Dougal Dobie, Rachel L. Webster, Roger J. Cappallo, Tara Murphy, Andrew Zic, Steve Croft, Stephen R. McWhirter, N. Udaya Shankar, Frank H. Briggs, Randall B. Wayth, Andrew Williams, Avinash A. Deshpande, Lincoln J. Greenhill, A. R. Offringa, Simon Johnston, High Energy Astrophys. & Astropart. Phys (API, FNWI), Kapteyn Astronomical Institute, ITA, USA, and AUS
Subjects: 010504 meteorology & atmospheric sciences, media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, Pulsar planet, FOS: Physical sciences, Murchison Widefield Array, Astrophysics, 01 natural sciences, Declination, Spectral line, Pulsar, Millisecond pulsar, pulsars: general, 0103 physical sciences, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, media_common, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Scintillation, Astronomy, Astronomy and Astrophysics, 13. Climate action, Space and Planetary Science, Sky, Astrophysics - High Energy Astrophysical Phenomena, radio continuum: stars
Abstract: We present 154 MHz Murchison Widefield Array imaging observations and variability information for a sample of pulsars. Over the declination range $-80^{\circ} < �� < 10^{\circ}$ we detect 17 known pulsars with mean flux density greater than 0.3 Jy. We explore the variability properties of this sample on timescales of minutes to years. For three of these pulsars, PSR J0953+0755, PSR J0437-4715 and PSR J0630-2834 we observe interstellar scintillation and variability on timescales of greater than 2 minutes. One further pulsar, PSR J0034-0721, showed significant variability, the physical origins of which are difficult to determine. The dynamic spectra for PSR J0953+0755 and PSR J0437-4715 show discrete time and frequency structure consistent with diffractive interstellar scintillation and we present the scintillation bandwidth and timescales from these observations. The remaining pulsars within our sample were statistically non-variable. We also explore the spectral properties of this sample and find spectral curvature in pulsars PSR J0835-4510, PSR J1752-2806 and PSR J0437-4715.
Published: 2016

86. Bayesian constraints on the global 21-cm signal from the Cosmic Dawn

Author: Danny C. Price, Jayce Dowell, Frank K. Schinzel, Jonathon Kocz, Gianni Bernardi, Steven W. Ellingson, Jonathan T. L. Zwart, Tarraneh Eftekhari, Lincoln J. Greenhill, Andrei Mesinger, ITA, USA, GBR, Bernardi, G., Zwart, J. T. L., Price, D., Greenhill, L. J., Mesinger, A., Dowell, J., Eftekhari, T., Ellingson, S. W., Kocz, J., and Schinzel, F.
Subjects: statistical [Methods], Cosmology and Nongalactic Astrophysics (astro-ph.CO), Diffuse radiation, FOS: Physical sciences, observation [Cosmology], Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, symbols.namesake, Settore FIS/05 - Astronomia e Astrofisica, 0103 physical sciences, Emission spectrum, 010303 astronomy & astrophysics, Reionization, Astrophysics::Galaxy Astrophysics, Physics, COSMIC cancer database, 010308 nuclear & particles physics, Astronomy, Astronomy and Astrophysics, Redshift, data analysi [Methods], Dark ages, reionization, first star, Dipole, Amplitude, Space and Planetary Science, symbols, Dark Ages, Gaussian network model, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The birth of the first luminous sources and the ensuing epoch of reionization are best studied via the redshifted 21-cm emission line, the signature of the first two imprinting the last. In this work we present a fully-Bayesian method, \textsc{hibayes}, for extracting the faint, global (sky-averaged) 21-cm signal from the much brighter foreground emission. We show that a simplified (but plausible), Gaussian model of the 21-cm emission from the Cosmic Dawn epoch ($15 \lesssim z \lesssim 30$), parameterized by an amplitude $A_{\rm HI}$, a frequency peak $��_{\rm HI}$ and a width $��_{\rm HI}$, can be extracted even in the presence of a structured foreground frequency spectrum (parameterized as a $7^{\rm th}$-order polynomial), provided sufficient signal-to-noise (400~hours of observation with a single dipole). We apply our method to an early, 19-minute long observation from the Large aperture Experiment to detect the Dark Ages, constraining the 21-cm signal amplitude and width to be $-890 < A_{\rm HI} < 0$ mK and $��_{\rm HI} > 6.5$ MHz (corresponding to $��z > 1.9$ at redshift $z \simeq 20$) respectively at the 95-per-cent confidence level in the range $13.2 < z < 27.4$ ($100 > ��> 50$ MHz)., 10 pages, 8 figures, MNRAS accepted
Published: 2016

87. Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

Author: J. van Leeuwen, Matthias Steinmetz, T. E. Hassall, A. Nelles, E. de Geus, M. Pilia, B. W. Stappers, Heino Falcke, H. J. A. Röttgering, Annalisa Bonafede, Oleg Smirnov, Anna V. Bilous, Satyendra Thoudam, Evan Keane, Peter G. Jonker, W. Frieswijk, Rudy Wijnands, A. Noutsos, M. Pietka, John D. Swinbank, Richard Fallows, R. J. van Weeren, M. Pandey-Pommier, Olaf Wucknitz, A. Alexov, Rebecca McFadden, E. Juette, F. Breitling, Stefan J. Wijnholds, Aris Karastergiou, Benedetta Ciardi, H. Paas, Antonia Rowlinson, Dominik J. Schwarz, Michael Kramer, A. I. F. Stewart, Y. Tang, Ashish Asgekar, K. Zagkouris, James A. Anderson, Chiara Ferrari, S. Duscha, James Miller-Jones, Andrew Lyne, Stefan Oslowski, Adam T. Deller, A. de Jong, R. C. Vermeulen, Gianni Bernardi, I. M. Avruch, M. A. Garrett, M. C. Toribio, Jochen Eislöffel, Charlotte Sobey, A. J. van der Horst, Rene P. Breton, Cyril Tasse, Marcus Brüggen, J. W. Broderick, Gerard H. Kuper, S. ter Veen, A. W. Gunst, Rob Fender, P. Zarka, D. McKay-Bukowski, Martin Bell, A. Horneffer, M. Kuniyoshi, Patrick Weltevrede, M. Serylak, A. G. Polatidis, Ralph A. M. J. Wijers, Mark J. Bentum, Christian Vocks, Jean-Mathias Grießmeier, Sera Markoff, Jason W. T. Hessels, Stephane Corbel, Laura Birzan, J. P. Hamaker, Wolfgang Reich, Michel Tagger, P. Maat, V. I. Kondratiev, George Heald, Gottfried Mann, R. Pizzo, Astronomy, Netherlands Institute for Radio Astronomy (ASTRON), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Vrije Universiteit Medical Centre (VUMC), Vrije Universiteit Amsterdam [Amsterdam] (VU), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), Oxford Astrophysics, University of Oxford, School of Physics and Astronomy [Southampton], University of Southampton, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University [Nijmegen], Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Centre for Astrophysics and Supercomputing [Swinburne] (CAS), Swinburne University of Technology [Melbourne], Department of Physics [Oxford], Max-Planck-Institut für Radioastronomie (MPIFR), Universität Bielefeld = Bielefeld University, University of Cape Town, Space Telescope Science Institute (STSci), Epidémiologie et Biostatistique [Bordeaux], Université Bordeaux Segalen - Bordeaux 2-Institut de Santé Publique, d'Épidémiologie et de Développement (ISPED)-Institut National de la Santé et de la Recherche Médicale (INSERM), SRON Netherlands Institute for Space Research (SRON), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, Leiden Observatory [Leiden], Universiteit Leiden [Leiden], University of Hamburg, Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), University of Edinburgh, Max-Planck-Institut für Astrophysik (MPA), Max-Planck-Gesellschaft, Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Structural Dynamics and Acoustics, University of Twente, Thüringer Landessternwarte Tautenburg (TLS), Institute of Mathematical and Physical Sciences, Department of Astrophysics [Oxford], Département de Géologie, Université de Montréal (UdeM), Astronomisches Institut der Ruhr-Universität Bochum, Ruhr-Universität Bochum [Bochum], Leibniz-Institut für Astrophysik Potsdam (AIP), Department of Physical Sciences, University of Oulu, University of Oulu, Curtin University [Perth], Planning and Transport Research Centre (PATREC), University of Groningen [Groningen], Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Australia Telescope National Facility (ATNF), Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Institute of Farm Animal Genetics (ING), Friedrich-Loeffler-Institut (FLI), SKA South Africa, Ska South Africa, Astrophysikalisches Institut Potsdam (AIP), Department of Physics [Dunedin], University of Otago [Dunedin, Nouvelle-Zélande], Princeton University, Edinburgh Research Station, Centre for Ecology and Hydrology, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Department of Astrophysics [Nijmegen], Radboud University [Nijmegen]-Radboud University [Nijmegen], Anton Pannekoek Institute for Astronomy, Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, Alexander von Humboldt Foundation Agence Nationale de la Recherche ANR-09-JCJC-0001-01, ANR-09-JCJC-0001,OPALES(2009), European Project: 337062,EC:FP7:ERC,ERC-2013-StG,DRAGNET(2014), European Project: 617199,EC:FP7:ERC,ERC-2013-CoG,ALERT(2014), European Project: 224838,EC:FP7:PEOPLE,FP7-PEOPLE-2007-4-3-IRG,PULSARS WITH LOFAR(2008), ROUCHON, Nathalie, Jeunes chercheuses et jeunes chercheurs - - OPALES2009 - ANR-09-JCJC-0001 - JCJC - VALID, DRAGNET: A high-speed, wide-angle camera for catching extreme astrophysical events - DRAGNET - - EC:FP7:ERC2014-01-01 - 2018-12-31 - 337062 - VALID, ALERT - The Apertif-LOFAR Exploration of the Radio Transient Sky - ALERT - - EC:FP7:ERC2014-12-01 - 2019-11-30 - 617199 - VALID, Radio pulsars with LOFAR: a study of extreme physics laboratories. - PULSARS WITH LOFAR - - EC:FP7:PEOPLE2008-05-01 - 2012-04-30 - 224838 - VALID, High Energy Astrophys. & Astropart. Phys (API, FNWI), University of Oxford [Oxford], Radboud university [Nijmegen], Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Fakultät für Physik, Universität Bielefeld, Universität Bielefeld, University of the Western Cape, Cape Town, Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), University of Twente [Netherlands], Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Radboud university [Nijmegen]-Radboud university [Nijmegen], Harvard University-Smithsonian Institution, Universiteit Leiden, École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Pilia, M., Hessels, J.W.T., Stappers, B.W., Kondratiev, V.I., Kramer, M., Van Leeuwen, J., Weltevrede, P., Lyne, A.G., Zagkouris, K., Hassall, T.E., Bilous, A.V., Breton, R.P., Falcke, H., Grießmeier, J.-M., Keane, E., Karastergiou, A., Kuniyoshi, M., Noutsos, A., Osłowski, S., Serylak, M., Sobey, C., Ter Veen, S., Alexov, A., Anderson, J., Asgekar, A., Avruch, I.M., Bell, M.E., Bentum, M.J., Bernardi, G., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J.W., Brüggen, M., Ciardi, B., Corbel, S., De Geus, E., De Jong, A., Deller, A., Duscha, S., Eislöffel, J., Fallows, R.A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M.A., Gunst, A.W., Hamaker, J.P., Heald, G., Horneffer, A., Jonker, P., Juette, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Miller-Jones, J.C.A., Nelles, A., Paas, H., Pandey-Pommier, M., Pietka, M., Pizzo, R., Polatidis, A.G., Reich, W., Röttgering, H., Rowlinson, A., Schwarz, D., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J.D., Tagger, M., Tang, Y., Tasse, C., Thoudam, S., Toribio, M.C., Van Der Horst, A.J., Vermeulen, R., Vocks, C., Van Weeren, R.J., Wijers, R.A.M.J., Wijnands, R., Wijnholds, S.J., Wucknitz, O., and Zarka, P.
Subjects: Astronomy, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, METIS-321663, Astrophysics::Cosmology and Extragalactic Astrophysics, Low frequency, 01 natural sciences, Radio spectrum, law.invention, Telescope, Radio telescope, [SDU] Sciences of the Universe [physics], stars: neutron, Pulsar, law, pulsars: general, 0103 physical sciences, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), IR-103184, Solar and Stellar Astrophysics (astro-ph.SR), Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, Astrophysics - Astrophysics of Galaxies, Interstellar medium, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Astrophysics of Galaxies (astro-ph.GA), ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Radio frequency, EWI-27451, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: LOFAR offers the unique capability of observing pulsars across the 10-240 MHz frequency range with a fractional bandwidth of roughly 50%. This spectral range is well-suited for studying the frequency evolution of pulse profile morphology caused by both intrinsic and extrinsic effects: such as changing emission altitude in the pulsar magnetosphere or scatter broadening by the interstellar medium, respectively. The magnitude of most of these effects increases rapidly towards low frequencies. LOFAR can thus address a number of open questions about the nature of radio pulsar emission and its propagation through the interstellar medium. We present the average pulse profiles of 100 pulsars observed in the two LOFAR frequency bands: High Band (120-167 MHz, 100 profiles) and Low Band (15-62 MHz, 26 profiles). We compare them with Westerbork Synthesis Radio Telescope (WSRT) and Lovell Telescope observations at higher frequencies (350 and1400 MHz) in order to study the profile evolution. The profiles are aligned in absolute phase by folding with a new set of timing solutions from the Lovell Telescope, which we present along with precise dispersion measures obtained with LOFAR. We find that the profile evolution with decreasing radio frequency does not follow a specific trend but, depending on the geometry of the pulsar, new components can enter into, or be hidden from, view. Nonetheless, in general our observations confirm the widening of pulsar profiles at low frequencies, as expected from radius-to-frequency mapping or birefringence theories. We offer this catalog of low-frequency pulsar profiles in a user friendly way via the EPN Database of Pulsar Profiles (http://www.epta.eu.org/epndb/)., Comment: 38 pages, 11 figures, 5 tables, A&A in press, updated with editorial corrections
Published: 2016

88. A Large-Scale, Low-Frequency Murchison Widefield Array Survey of Galactic H ii Regions between 260 < l < 340

Author: K. S. Dwarakanath, Chen Wu, Daniel A. Mitchell, Divya Oberoi, John Morgan, Martin Bell, Miguel F. Morales, Andrew Williams, Bryna J. Hazelton, Bryan Gaensler, Judd D. Bowman, Joseph R. Callingham, Gianni Bernardi, Lincoln J. Greenhill, Lister Staveley-Smith, Melanie Johnston-Hollitt, Ravi Subrahmanyan, Natasha Hurley-Walker, Paul Hancock, Avinash A. Deshpande, Steven Tingay, Emil Lenc, Anna D. Kapińska, Luke Hindson, Colin J. Lonsdale, Thiagaraj Prabu, Bi-Qing For, Chrysanthi Williams, N. Udaya Shankar, A. R. Offringa, K. S. Srivani, Eric R. Morgan, David L. Kaplan, Randall B. Wayth, Pietro Procopio, Frank H. Briggs, Rachel L. Webster, Qinghua Zheng, Stephen R. McWhirter, H. Su, Stephen M. Ord, Roger J. Cappallo, Benjamin McKinley, ITA, USA, and AUS
Subjects: Physics, 010308 nuclear & particles physics, Space and Planetary Science, 0103 physical sciences, Library science, Astronomy and Astrophysics, Murchison Widefield Array, Subject (documents), Creative commons, Astrophysics - Astrophysics of Galaxies, 010303 astronomy & astrophysics, 01 natural sciences, License
Abstract: We have compiled a catalogue of HII regions detected with the Murchison Widefield Array (MWA) between 72 and 231MHz. The multiple frequency bands provided by the MWA allow us identify the characteristic spectrum generated by the thermal Bremsstrahlung process in HII regions. We detect 302 HII regions between 260 < l < 340 and report on the positions, sizes, peak, integrated flux density, and spectral indices of these HII regions. By identifying the point at which HII regions transition from the optically thin to thick regime we derive the physical properties including the electron density, ionised gas mass and ionising photon flux, towards 61 HII regions. This catalogue of HII regions represents the most extensive and uniform low frequency survey of HII regions in the Galaxy to date., Comment: 20 pages, 9 figures, 3 tables
Published: 2016

89. LOFAR MSSS: detection of a low-frequency radio transient in 400 h of monitoring of the North Celestial Pole

Author: Rebecca McFadden, Martin Bell, Sera Markoff, G. Kokotanekov, R. J. van Weeren, D. McKay-Bukowski, James M. Anderson, Jason W. T. Hessels, Peter G. Jonker, Ralph A. M. J. Wijers, H. Munk, Casey J. Law, Frank Breitling, B. Scheers, Marcus Brüggen, M. C. Toribio, A. Horneffer, George Heald, M. A. Garrett, Aris Karastergiou, Luke Pratley, Rudy Wijnands, Y. Cendes, F. de Gasperin, A. Alexov, Michael W. Wise, Gianni Bernardi, Jörg R. Hörandel, B. Ciardi, M. Kuniyoshi, James Miller-Jones, J. van Leeuwen, T. Munoz-Darias, Aleksandar Shulevski, John McKean, J.-M. Grießmeier, John D. Swinbank, Jochen Eislöffel, P. Maat, Cyril Tasse, Wilfred Frieswijk, M. J. Norden, J. W. Broderick, A. G. Polatidis, Arthur Corstanje, T E Hassall, Heino Falcke, Harvey Butcher, E. de Geus, V. I. Kondratiev, E. Juette, Anna M. M. Scaife, M. Pandey-Pommier, Benjamin Stappers, H. Paas, A. W. Gunst, I. M. Avruch, Volker Heesen, D. Carbone, Mark J. Bentum, Antonia Rowlinson, Annalisa Bonafede, Rob Fender, J. Sluman, E. Rol, Matthias Steinmetz, Chiara Ferrari, Gijs Molenaar, S. Duscha, G. Kuper, D. D. Mulcahy, Sarod Yatawatta, Philip Best, M. Pietka, H. J. A. Röttgering, Satyendra Thoudam, A. O. Clarke, Adam Stewart, M. P. van Haarlem, Charlotte Sobey, M. Iacobelli, Olaf Wucknitz, Matthias Hoeft, Emanuela Orrú, M. Loose, Ph. Zarka, Adam Deller, Martin J. Hardcastle, Tim D. Staley, Ashish Asgekar, J. Moldon, Dominik J. Schwarz, A. J. van der Horst, Christian Vocks, Rene P. Breton, John Conway, Stephane Corbel, R. C. Vermeulen, Stefan J. Wijnholds, S. van Velzen, T. L. Grobler, Oleg Smirnov, Astronomy, Laboratory for Atmospheric and Space Physics [Boulder] (LASP), University of Colorado [Boulder], University of Southampton, Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], School of Physics and Astronomy [Southampton], Netherlands Institute for Radio Astronomy (ASTRON), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), Oxford Astrophysics, University of Oxford [Oxford], Rhodes University, Grahamstown, CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Jacobs University [Bremen], Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Unité Scientifique de la Station de Nançay (USN), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Universität Hamburg (UHH), Thüringer Landessternwarte Tautenburg (TLS), Radboud university [Nijmegen], Département de Géologie, Université de Montréal [Montréal], Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), University of Hertfordshire [Hatfield] (UH), Max-Planck-Institut für Radioastronomie (MPIFR), Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Curtin University [Perth], Planning and Transport Research Centre (PATREC), Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Victoria University of Wellington, Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], SKA South Africa, Ska South Africa, Galaxies, Etoiles, Physique, Instrumentation (GEPI), PSL Research University (PSL)-PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Department of Mathematics, The George Washington University, Washington State University (WSU), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, Anton Pannekoek Institute for Astronomy, Observatoire de Paris - Site de Paris (OP), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Institute for Mathematics Applied to Geoscience, National Center for Atmospheric Research [Boulder] (NCAR), SRON Netherlands Institute for Space Research (SRON), Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), University of Edinburgh, Leibniz-Institut für Astrophysik Potsdam (AIP), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Onsala Space Observatory, Dept. of Radio and Space Science, Chalmers University of Technology, Chalmers University of Technology [Göteborg], Ruhr-Universität Bochum [Bochum], University of Oulu, The Netherlands Institute for Radio Astronomy (ASTRON), 7990-AA Dwingeloo, Netherlands, Departament d'Astronomia i Meteorologia [Barcelona], Institut de Ciènces del Cosmos (ICC), Universitat de Barcelona (UB)-Universitat de Barcelona (UB), Center for Information Technology CIT, Université de Groningen, Interactions Son Musique Mouvement, Sciences et Technologies de la Musique et du Son (STMS), Université Pierre et Marie Curie - Paris 6 (UPMC)-IRCAM-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-IRCAM-Centre National de la Recherche Scientifique (CNRS), Rhodes University, Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), Finca El Encin, Instituto Madrileño de Investigación y Desarrollo Rural, Agrario y Alimentario (IMIDRA), Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, High Energy Astrophys. & Astropart. Phys (API, FNWI), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO), Université de Montréal (UdeM), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Department of Mathematics [George Washington University] (GW), The George Washington University (GW), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Pierre et Marie Curie - Paris 6 (UPMC), Universitat de Barcelona (UB), Institut de Recherche et Coordination Acoustique/Musique (IRCAM)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche et Coordination Acoustique/Musique (IRCAM)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), University of Oxford, Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Radboud University [Nijmegen], Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Universiteit Leiden, École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Harvard University-Smithsonian Institution, Stewart, A.J., Fender, R.P., Broderick, J.W., Hassall, T.E., Muñoz-Darias, T., Rowlinson, A., Swinbank, J.D., Staley, T.D., Molenaar, G.J., Scheers, B., Grobler, T.L., Pietka, M., Heald, G., McKean, J.P., Bell, M.E., Bonafede, A., Breton, R.P., Carbone, D., Cendes, Y., Clarke, A.O., Corbel, S., De Gasperin, F., Eislöffel, J., Falcke, H., Ferrari, C., Grießmeier, J.-M., Hardcastle, M.J., Heesen, V., Hessels, J.W.T., Horneffer, A., Iacobelli, M., Jonker, P., Karastergiou, A., Kokotanekov, G., Kondratiev, V.I., Kuniyoshi, M., Law, C.J., van Leeuwen, J., Markoff, S., Miller-Jones, J.C.A., Mulcahy, D., Orru, E., Pandey-Pommier, M., Pratley, L., Rol, E., Röttgering, H.J.A., Scaife, A.M.M., Shulevski, A., Sobey, C.A., Stappers, B.W., Tasse, C., van der Horst, A.J., van Velzen, S., van Weeren, R.J., Wijers, R.A.M.J., Wijnands, R., Wise, M., Zarka, P., Alexov, A., Anderson, J., Asgekar, A., Avruch, I.M., Bentum, M.J., Bernardi, G., Best, P., Breitling, F., Brüggen, M., Butcher, H.R., Ciardi, B., Conway, J.E., Corstanje, A., de Geus, E., Deller, A., Duscha, S., Frieswijk, W., Garrett, M.A., Gunst, A.W., Van Haarlem, M.P., Hoeft, M., Hörandel, J., Juette, E., Kuper, G., Loose, M., Maat, P., McFadden, R., McKay-Bukowski, D., Moldon, J., Munk, H., Norden, M.J., Paas, H., Polatidis, A.G., Schwarz, D., Sluman, J., Smirnov, O., Steinmetz, M., Thoudam, S., Toribio, M.C., Vermeulen, R., Vocks, C., Wijnholds, S.J., Wucknitz, O., Yatawatta, S., ITA, GBR, FRA, DEU, and NLD
Subjects: Astronomy, media_common.quotation_subject, interferometers [instrumentation], radio continuum: general, FOS: Physical sciences, techniques: image processing, 02 engineering and technology, Astrophysics, Low frequency, 01 natural sciences, Instrumentation: interferometer, Celestial pole, 0103 physical sciences, IR-102656, 0202 electrical engineering, electronic engineering, information engineering, instrumentation: interferometers, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, media_common, EWI-27481, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, image processing [techniques], METIS-320906, 020206 networking & telecommunications, Astronomy and Astrophysics, LOFAR, Limiting, Astronomy and Astrophysic, instrumentation: interferometers – techniques: image processing – radio continuum: general, radio, continuum: general, Observation duration, Space and Planetary Science, Sky, [SDU]Sciences of the Universe [physics], ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, general [radio continuum], Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: We present the results of a four-month campaign searching for low-frequency radio transients near the North Celestial Pole with the Low-Frequency Array (LOFAR), as part of the Multifrequency Snapshot Sky Survey (MSSS). The data were recorded between 2011 December and 2012 April and comprised 2149 11-minute snapshots, each covering 175 deg^2. We have found one convincing candidate astrophysical transient, with a duration of a few minutes and a flux density at 60 MHz of 15-25 Jy. The transient does not repeat and has no obvious optical or high-energy counterpart, as a result of which its nature is unclear. The detection of this event implies a transient rate at 60 MHz of 3.9 (+14.7, -3.7) x 10^-4 day^-1 deg^-2, and a transient surface density of 1.5 x 10^-5 deg^-2, at a 7.9-Jy limiting flux density and ~10-minute time-scale. The campaign data were also searched for transients at a range of other time-scales, from 0.5 to 297 min, which allowed us to place a range of limits on transient rates at 60 MHz as a function of observation duration., 23 pages, 16 figures, 5 tables, accepted for publication in MNRAS
Published: 2016

90. Hydrogen Epoch of Reionization Array (HERA)

Author: Paul Alexander, Lourence Malan, David MacMahon, Daniel C. Jacobs, Jon Ringuette, C. H. Smith, Angelo Syce, Cresshim Malgas, Aaron R. Parsons, Nicolas Fagnoni, Joshua S. Dillon, Miguel F. Morales, Nithyanandan Thyagarajan, Richard F. Bradley, Peter Williams, Zaki S. Ali, Telalo Lekalake, Aaron Ewall-Wice, Nipanjana Patra, Eloy de Lera Acedo, Jonathan C. Pober, Nathan Mathison, Andrei Mesinger, Nima Razavi-Ghods, Gianni Bernardi, Bradley Greig, Steve R. Furlanetto, Jasper Grobbelaar, David DeBoer, Adrian Liu, Matthys Maree, Saul A. Kohn, Zachary E. Martinot, Anita Loots, Brian Glendenning, Carina Cheng, Judd D. Bowman, Raddwine Sell, Kathryn Rosie, Samantha Pieterse, Adam P. Beardsley, Gcobisa Fadana, Bryna J. Hazelton, Jacqueline N. Hewitt, Haoxuan Zheng, James E. Aguirre, James Robnett, Abraham R. Neben, Randall Fritz, Austin Julius, Chris L. Carilli, Jack Hickish, Eunice Matsetela, MacCalvin Kariseb, Max Tegmark, ITA, USA, Deboer, David R., Parsons, Aaron R., Aguirre, James E., Alexander, Paul, Ali, Zaki S., Beardsley, Adam P., Bernardi, Gianni, Bowman, Judd D., Bradley, Richard F., Carilli, Chris L., Cheng, Carina, Acedo, Eloy de Lera, Dillon, Joshua S., Ewall-Wice, Aaron, Fadana, Gcobisa, Fagnoni, Nicola, Fritz, Randall, Furlanetto, Steve R., Glendenning, Brian, Greig, Bradley, Grobbelaar, Jasper, Hazelton, Bryna J., Hewitt, Jacqueline N., Hickish, Jack, Jacobs, Daniel C., Julius, Austin, Kariseb, Maccalvin, Kohn, Saul A., Lekalake, Telalo, Liu, Adrian, Loots, Anita, Macmahon, David, Malan, Lourence, Malgas, Cresshim, Maree, Matthy, Martinot, Zachary, Mathison, Nathan, Matsetela, Eunice, Mesinger, Andrei, Morales, Miguel F., Neben, Abraham R., Patra, Nipanjana, Pieterse, Samantha, Pober, Jonathan C., Razavi-Ghods, Nima, Ringuette, Jon, Robnett, Jame, Rosie, Kathryn, Sell, Raddwine, Smith, Craig, Syce, Angelo, Tegmark, Max, Thyagarajan, Nithyanandan, Williams, Peter K. G., and Zheng, Haoxuan
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Bryna, Dark age, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, 7. Clean energy, 01 natural sciences, Reionization, Settore FIS/05 - Astronomia e Astrofisica, First star, 0103 physical sciences, Physical Sciences and Mathematics, Theology, Telescope, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Astrophysics::Galaxy Astrophysics, biology, 010308 nuclear & particles physics, Philosophy, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, HERA, biology.organism_classification, Space and Planetary Science, Interferometer [Instrumentation], Interferometric [Techniques], Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to measure 21 cm emission from the primordial intergalactic medium (IGM) throughout cosmic reionization ($z=6-12$), and to explore earlier epochs of our Cosmic Dawn ($z\sim30$). During these epochs, early stars and black holes heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is designed to characterize the evolution of the 21 cm power spectrum to constrain the timing and morphology of reionization, the properties of the first galaxies, the evolution of large-scale structure, and the early sources of heating. The full HERA instrument will be a 350-element interferometer in South Africa consisting of 14-m parabolic dishes observing from 50 to 250 MHz. Currently, 19 dishes have been deployed on site and the next 18 are under construction. HERA has been designated as an SKA Precursor instrument. In this paper, we summarize HERA's scientific context and provide forecasts for its key science results. After reviewing the current state of the art in foreground mitigation, we use the delay-spectrum technique to motivate high-level performance requirements for the HERA instrument. Next, we present the HERA instrument design, along with the subsystem specifications that ensure that HERA meets its performance requirements. Finally, we summarize the schedule and status of the project. We conclude by suggesting that, given the realities of foreground contamination, current-generation 21 cm instruments are approaching their sensitivity limits. HERA is designed to bring both the sensitivity and the precision to deliver its primary science on the basis of proven foreground filtering techniques, while developing new subtraction techniques to unlock new capabilities. The result will be a major step toward realizing the widely recognized scientific potential of 21 cm cosmology., Comment: 26 pages, 24 figures, 2 tables
Published: 2016
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91. CHIPS: The Cosmological HI Power Spectrum Estimator

Author: J. Riding, Chen Wu, Bryna J. Hazelton, Judd D. Bowman, Ian Sullivan, Eric R. Morgan, Joshua S. Dillon, L. J. Greenhill, Natasha Hurley-Walker, David L. Kaplan, Emil Lenc, A. de Oliveira-Costa, A. P. Beardsley, Steven Tingay, Divya Oberoi, Randall B. Wayth, Rachel L. Webster, J. S. B. Wyithe, C. J. Lonsdale, P. Carroll, Shiv K. Sethi, A. R. Offringa, K. S. Srivani, Daniel A. Mitchell, Max Tegmark, Jacqueline N. Hewitt, Pietro Procopio, Thiagaraj Prabu, Abraham R. Neben, Chrysanthi Williams, Aaron Ewall-Wice, Daniel C. Jacobs, J. L. B. Line, Melanie Johnston-Hollitt, B. Pindor, Stephen M. Ord, Nithyanandan Thyagarajan, F. Briggs, Lu Feng, N. Udaya Shankar, Benjamin McKinley, Andrew R. Williams, Gianni Bernardi, Avi Loeb, Nichole Barry, Ravi Subrahmanyan, S. Paul, Roger J. Cappallo, Cathryn M. Trott, Miguel F. Morales, Jonathan C. Pober, Han-Seek Kim, and AUS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Estimator, Spectral density, FOS: Physical sciences, Astronomy and Astrophysics, Murchison Widefield Array, Astrophysics::Cosmology and Extragalactic Astrophysics, Parameter space, 01 natural sciences, Redshift, Weighting, Radio telescope, Space and Planetary Science, 0103 physical sciences, Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, Reionization, Algorithm, Instrumentation and Methods for Astrophysics (astro-ph.IM), Mathematics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Detection of the cosmological neutral hydrogen signal from the Epoch of Reionization, and estimation of its basic physical parameters, is the principal scientific aim of many current low-frequency radio telescopes. Here we describe the Cosmological HI Power Spectrum Estimator (CHIPS), an algorithm developed and implemented with data from the Murchison Widefield Array (MWA), to compute the two-dimensional and spherically-averaged power spectrum of brightness temperature fluctuations. The principal motivations for CHIPS are the application of realistic instrumental and foreground models to form the optimal estimator, thereby maximising the likelihood of unbiased signal estimation, and allowing a full covariant understanding of the outputs. CHIPS employs an inverse-covariance weighting of the data through the maximum likelihood estimator, thereby allowing use of the full parameter space for signal estimation ("foreground suppression"). We describe the motivation for the algorithm, implementation, application to real and simulated data, and early outputs. Upon application to a set of 3 hours of data, we set a 2$\sigma$ upper limit on the EoR dimensionless power at $k=0.05$~h.Mpc$^{-1}$ of $\Delta_k^2, Comment: 34 pages, accepted for publication in ApJ
Published: 2016
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92. CONSTRAINING POLARIZED FOREGROUNDS FOR EoR EXPERIMENTS. I. 2D POWER SPECTRA FROM THE PAPER-32 IMAGING ARRAY

Author: Nicole E. Gugliucci, Richard F. Bradley, James E. Aguirre, David F. Moore, P. Klima, Daniel C. Jacobs, Saul A. Kohn, Irina I. Stefan, Aaron R. Parsons, D. MacMahon, Gianni Bernardi, Jonathan C. Pober, D. R. DeBoer, Chris Carilli, Chuneeta D. Nunhokee, William P. Walbrugh, Zaki S. Ali, Jason Manley, ITA, USA, and ZAF
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Spectral line, symbols.namesake, Optics, 0103 physical sciences, Faraday effect, Astronomical interferometer, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Reionization, Physics, Line-of-sight, 010308 nuclear & particles physics, business.industry, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Polarization (waves), Interferometry, Space and Planetary Science, Frequency domain, symbols, Astrophysics - Instrumentation and Methods for Astrophysics, business, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Current-generation low frequency interferometers constructed with the objective of detecting the high-redshift 21 cm background, aim to generate power spectra of the brightness-temperature contrast of neutral hydrogen in primordial intergalactic medium. Two-dimensional power spectra (power in Fourier modes parallel and perpendicular to the line of sight) formed from interferometric visibilities have been shown to delineate a boundary between spectrally-smooth foregrounds (known as the wedge) and spectrally-structured 21 cm background emission (the EoR-window). However, polarized foregrounds are known to possess spectral structure due to Faraday rotation, which can leak into the EoR window. In this work, we create and analyze 2D power spectra from the PAPER-32 imaging array in Stokes I, Q, U and V. These allow us to observe and diagnose systematic effects in our calibration at high signal-to-noise within the Fourier space most relevant to EoR experiments. We observe well-defined windows in the Stokes visibilities, with Stokes Q, U and V power spectra sharing a similar wedge shape to that seen in Stokes I. With modest polarization calibration, we see no evidence that polarization calibration errors move power outside the wedge in any Stokes visibility, to the noise levels attained. Deeper integrations will be required to confirm that this behavior persists to the depth required for EoR detection., 10 pages, 7 figures, accepted by ApJ
Published: 2016

93. The Murchison Widefield Array 21 cm Power Spectrum Analysis Methodology

Author: Cathryn M. Trott, Miguel F. Morales, Adam P. Beardsley, Frank H. Briggs, S. R. McWhirter, Bryan Gaensler, Aaron Ewall-Wice, Edward H. Morgan, J. L. B. Line, J. S. B. Wyithe, E. Kratzenberg, Andrew Williams, David Emrich, Lu Feng, Nithyanandan Thyagarajan, Mervyn J. Lynch, Steven Tingay, Alan E. E. Rogers, Rachel L. Webster, S. Paul, N. Udaya Shankar, Daniel A. Mitchell, Nichole Barry, Roger J. Cappallo, K. S. Srivani, J. Riding, Ian Sullivan, Judd D. Bowman, Joshua S. Dillon, Han-Seek Kim, Lincoln J. Greenhill, A. R. Offringa, Christopher L. Williams, Pietro Procopio, Chen Wu, David L. Kaplan, B. E. Corey, Abraham Loeb, Justin C. Kasper, Gianni Bernardi, T. Prabu, Shiv K. Sethi, Divya Oberoi, Jacqueline N. Hewitt, Mark Waterson, Bartosz Pindor, Ravi Subrahmanyan, A. R. Whitney, A. de Oliveira-Costa, R. Goeke, Natasha Hurley-Walker, Emil Lenc, A. Roshi, Abraham R. Neben, Daniel C. Jacobs, Bryna J. Hazelton, Colin J. Lonsdale, P. Carroll, Jonathan C. Pober, Stephen M. Ord, Benjamin McKinley, Max Tegmark, Melanie Johnston-Hollitt, Randall B. Wayth, ITA, USA, and AUS
Subjects: Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010308 nuclear & particles physics, Calibration (statistics), media_common.quotation_subject, Astrophysics::Instrumentation and Methods for Astrophysics, Spectral density, FOS: Physical sciences, Astronomy and Astrophysics, Murchison Widefield Array, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Power (physics), Reduction (complexity), Space and Planetary Science, Sky, 0103 physical sciences, Range (statistics), Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, Reionization, Algorithm, Instrumentation and Methods for Astrophysics (astro-ph.IM), media_common, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present the 21 cm power spectrum analysis approach of the Murchison Widefield Array Epoch of Reionization project. In this paper, we compare the outputs of multiple pipelines for the purpose of validating statistical limits cosmological hydrogen at redshifts between 6 and 12. Multiple, independent, data calibration and reduction pipelines are used to make power spectrum limits on a fiducial night of data. Comparing the outputs of imaging and power spectrum stages highlights differences in calibration, foreground subtraction and power spectrum calculation. The power spectra found using these different methods span a space defined by the various tradeoffs between speed, accuracy, and systematic control. Lessons learned from comparing the pipelines range from the algorithmic to the prosaically mundane; all demonstrate the many pitfalls of neglecting reproducibility. We briefly discuss the way these different methods attempt to handle the question of evaluating a significant detection in the presence of foregrounds., Comment: accepted to ApJ
Published: 2016

94. Radio recombination lines from obscured quasars with the SKA

Author: Andrea Ferrara, Chiara Feruglio, L. Graziani, Simona Gallerani, Gianni Bernardi, Serena Manti, Manti, Serena, Gallerani, Simona, Ferrara, Andrea, Feruglio, Chiara, Graziani, Luca, and Bernardi, Gianni
Subjects: Absolute magnitude, Photon, astro-ph.GA, FOS: Physical sciences, Astrophysics, Radiation, Galaxy: formation, H II regions, Quasars: emission lines, 01 natural sciences, Settore FIS/05 - Astronomia e Astrofisica, 0103 physical sciences, Galaxy formation and evolution, Stimulated emission, 010303 astronomy & astrophysics, Line (formation), Physics, 010308 nuclear & particles physics, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics - Astrophysics of Galaxies, Redshift, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA)
Abstract: We explore the possibility of detecting hydrogen radio recombination lines from 0 < z < 10 quasars. We compute the expected Hnalpha flux densities as a function of absolute magnitude and redshift by considering (i) the range of observed AGN spectral indices from UV to X-ray bands, (ii) secondary ionizations from X-ray photons, and (iii) stimulated emission due to nonthermal radiation. All these effects are important to determine the line fluxes. We find that the combination of slopes: alpha_X,hard = -1.11, alpha_X,soft = -0.7, alpha_EUV = -1.3, alpha_UV = -1.7, maximizes the expected flux, f_Hnalpha = 10 microJy for z = 7 quasars with M_AB = -27 in the n = 50 lines; allowed SED variations produce variations by a factor of 3 around this value. Secondaries boost the line intensity by a factor of 2 to 4, while stimulated emission in high-z quasars with M_AB = -26 provides an extra boost to RRL flux observed at nu = 1 GHz if recombinations arise in HII regions with T_e = 10^3-5 K, n_e = 10^3-5 cm^-3. We compute the sensitivity required for a 5sigma detection of Hnalpha lines using the SKA, finding that the SKA-MID could detect sources with M_AB < -27 (M_AB < -26) at z < 8 (z < 3) in less than 100 hrs of observing time. These observations could open new paths to searches for obscured SMBH progenitors, complementing X-ray, optical/IR and sub-mm surveys., 11 pages, 9 figures; to be published in Monthly Notices of the Royal Astronomical Society Main Journal
Published: 2016

95. Beam-forming Errors in Murchison Widefield Array Phased Array Antennas and their Effects on Epoch of Reionization Science

Author: Stephen R. McWhirter, Roger J. Cappallo, Jacqueline N. Hewitt, K. S. Srivani, Rachel L. Webster, Robert F. Goeke, Judd D. Bowman, Ravi Subrahmanyan, Stephen M. Ord, Bryna J. Hazelton, N. Udaya Shankar, Steven Tingay, Colin J. Lonsdale, Brian E. Corey, Divya Oberoi, Andrew Williams, Avinash A. Deshpande, Frank H. Briggs, Gianni Bernardi, David L. Kaplan, Lincoln J. Greenhill, Abraham R. Neben, Daniel A. Mitchell, Thiagaraj Prabu, Christopher L. Williams, Eric R. Morgan, Joshua S. Dillon, Miguel F. Morales, Richard F. Bradley, Randall B. Wayth, Melanie Johnston-Hollitt, ITA, USA, and AUS
Subjects: Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010308 nuclear & particles physics, Main lobe, business.industry, Phased array, Astrophysics::Instrumentation and Methods for Astrophysics, Spectral density, FOS: Physical sciences, Astronomy and Astrophysics, Murchison Widefield Array, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Redshift, Optics, Space and Planetary Science, 0103 physical sciences, Dark Ages, Antenna (radio), Astrophysics - Instrumentation and Methods for Astrophysics, business, 010303 astronomy & astrophysics, Reionization, Instrumentation and Methods for Astrophysics (astro-ph.IM), Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Accurate antenna beam models are critical for radio observations aiming to isolate the redshifted 21cm spectral line emission from the Dark Ages and the Epoch of Reionization and unlock the scientific potential of 21cm cosmology. Past work has focused on characterizing mean antenna beam models using either satellite signals or astronomical sources as calibrators, but antenna-to-antenna variation due to imperfect instrumentation has remained unexplored. We characterize this variation for the Murchison Widefield Array (MWA) through laboratory measurements and simulations, finding typical deviations of order +/- 10-20% near the edges of the main lobe and in the sidelobes. We consider the ramifications of these results for image- and power spectrum-based science. In particular, we simulate visibilities measured by a 100m baseline and find that using an otherwise perfect foreground model, unmodeled beamforming errors severely limit foreground subtraction accuracy within the region of Fourier space contaminated by foreground emission (the "wedge"). This region likely contains much of the cosmological signal, and accessing it will require measurement of per-antenna beam patterns. However, unmodeled beamforming errors do not contaminate the Fourier space region expected to be free of foreground contamination (the "EOR window"), showing that foreground avoidance remains a viable strategy., Comment: Accepted to ApJ
Published: 2016

96. The EoR sensitivity of the Murchison Widefield Array

Author: J. S. B. Wyithe, Robert F. Goeke, Edward H. Morgan, Mervyn J. Lynch, Steven Tingay, Alan E. E. Rogers, Ravi Subrahmanyan, David Emrich, Brian E. Corey, John D. Bunton, Melanie Johnston-Hollitt, B. B. Kincaid, Judd D. Bowman, Ron Remillard, Miguel F. Morales, A. Roshi, R. Koenig, Christopher L. Williams, Colin J. Lonsdale, Stephen R. McWhirter, Joseph Pathikulangara, David G. Barnes, Randall B. Wayth, David Herne, Daniel A. Mitchell, L. deSouza, Alan R. Whitney, Justin C. Kasper, K. S. Srivani, Rachel L. Webster, Jacqueline N. Hewitt, Mark Waterson, Stephen M. Ord, Roger J. Cappallo, Divya Oberoi, Robert J. Sault, Thiagaraj Prabu, Jamie Stevens, Joseph E. Salah, Andrew Williams, Avinash A. Deshpande, Shankar N. Udaya, Gianni Bernardi, Lincoln J. Greenhill, Eric Kratzenberg, David L. Kaplan, Bryna J. Hazelton, Bryan Gaensler, Adam P. Beardsley, W. Arcus, Frank H. Briggs, Haystack Observatory, MIT Kavli Institute for Astrophysics and Space Research, Cappallo, Roger J., Corey, Brian E., Goeke, Robert F., Hewitt, Jacqueline N., Kincaid, Barton B., Kratzenberg, Eric W., Lonsdale, Colin John, McWhirter, Stephen R., Morgan, Edward H., Oberoi, Divya, Remillard, Ronald Alan, Rogers, Alan E. E., Salah, J. E., Whitney, Alan R., and Williams, Christopher Leigh
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), FOS: Physical sciences, Murchison Widefield Array, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Optics, 0103 physical sciences, Astronomical interferometer, Sensitivity (control systems), Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Reionization, Physics, 010308 nuclear & particles physics, business.industry, Astrophysics::Instrumentation and Methods for Astrophysics, Spectral density, Astronomy and Astrophysics, Redshift, Space and Planetary Science, Antenna (radio), Astrophysics - Instrumentation and Methods for Astrophysics, Fiducial marker, business, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Using the final 128 antenna locations of the Murchison Widefield Array (MWA), we calculate its sensitivity to the epoch of reionization (EoR) power spectrum of redshifted 21 cm emission for a fiducial model and provide the tools to calculate the sensitivity for any model. Our calculation takes into account synthesis rotation, chromatic and asymmetrical baseline effects, and excludes modes that will be contaminated by foreground subtraction. For the fiducial model, the MWA will be capable of a 14σ detection of the EoR signal with one full season of observation on two fields (900 and 700 h)., National Science Foundation (U.S.) (Grant AST CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant AST-0908884), National Science Foundation (U.S.) (Grant PHY-0835713), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science
Published: 2012

97. Imaging neutral hydrogen on large scales during the Epoch of Reionization with LOFAR

Author: Michiel A. Brentjens, Gianni Bernardi, Garrelt Mellema, Sarod Yatawatta, S. Daiboo, Harish Vedantham, Benedetta Ciardi, O. Martinez-Rubi, S. Kazemi, V. N. Pandey, Geraint Harker, Joop Schaye, P. Labropolous, de Antonius Bruyn, Saleem Zaroubi, Rajat M. Thomas, V. Veligatla, Léon V. E. Koopmans, A. R. Offringa, and Vibor Jelić
Subjects: Physics, 010308 nuclear & particles physics, Astronomy and Astrophysics, Field of view, Scale (descriptive set theory), Astrophysics::Cosmology and Extragalactic Astrophysics, LOFAR, Astrophysics, 01 natural sciences, 7. Clean energy, Degree (music), Redshift, Space and Planetary Science, 0103 physical sciences, Sensitivity (control systems), 010303 astronomy & astrophysics, Reionization, Coherence (physics)
Abstract: The first generation of redshifted 21 cm detection experiments, carried out with arrays like LOFAR, MWA and GMRT, will have a very low signal-to-noise ratio per resolution element (\sim 0.2). In addition, whereas the variance of the cosmological signal decreases on scales larger than the typical size of ionization bubbles, the variance of the formidable galactic foregrounds increases, making it hard to disentangle the two on such large scales. The poor sensitivity on small scales on the one hand, and the foregrounds effect on large scales on the other hand, make direct imaging of the Epoch of Reionization of the Universe very difficult, and detection of the signal therefore is expected to be statistical.Despite these hurdles, in this paper we argue that for many reionization scenarios low resolution images could be obtained from the expected data. This is because at the later stages of the process one still finds very large pockets of neutral regions in the IGM, reflecting the clustering of the large-scale structure, which stays strong up to scales of \sim 120 comoving Mpc/h (\sim 1 degree). The coherence of the emission on those scales allows us to reach sufficient S/N (\sim 3) so as to obtain reionization 21 cm images. Such images will be extremely valuable for answering many cosmological questions but above all they will be a very powerful tool to test our control of the systematics in the data. The existence of this typical scale (\sim 120 comoving Mpc/h) also argues for designing future EoR experiments, e.g., with SKA, with a field of view of at least 4 degree.
Published: 2012

98. A new layout optimization technique for interferometric arrays, applied to the Murchison Widefield Array

Author: Rachel L. Webster, John D. Bunton, Ron Remillard, Roger C. Cappallo, Thiagaraj Prabu, Eric Kratzenberg, Gianni Bernardi, Eric R. Morgan, Miguel F. Morales, Stephen M. Ord, Andrew Williams, Avinash A. Deshpande, Judd D. Bowman, W. Arcus, Christopher L. Williams, A. Roshi, M. J. Lynch, Colin J. Lonsdale, N. Uday Shankar, R. Koeing, David L. Kaplan, L. J. Greenhill, Divya Oberoi, Robert F. Goeke, Stephen R. McWhirter, David G. Barnes, Robert J. Sault, Bryna J. Hazelton, Bryan Gaensler, M. Waterson, Brian E. Corey, Alan R. Whitney, Joseph Pathikulangara, David Herne, Jacqueline N. Hewitt, Daniel A. Mitchell, Jamie Stevens, Steven Tingay, Alan E. E. Rogers, J. C. Kasper, R. B. Wayth, L. deSouza, Ravi Subrahmanyan, J. S. B. Wyithe, Joseph E. Salah, A. P. Beardsley, David Emrich, B. B. Kincaid, and K. S. Srivani
Subjects: Point spread function, 010308 nuclear & particles physics, Computer science, Astronomy and Astrophysics, Murchison Widefield Array, 01 natural sciences, Interferometry, Space and Planetary Science, 0103 physical sciences, Astronomical interferometer, Antenna (radio), Baseline (configuration management), 010303 astronomy & astrophysics, Algorithm
Abstract: Antenna layout is an important design consideration for radio interferometers because it determines the quality of the snapshot point spread function (PSF, or array beam). This is particularly true for experiments targeting the 21 cm Epoch of Reionization signal as the quality of the foreground subtraction depends directly on the spatial dynamic range and thus the smoothness of the baseline distribution. Nearly all sites have constraints on where antennas can be placed---even at the remote Australian location of the MWA (Murchison Widefield Array) there are rock outcrops, flood zones, heritages areas, emergency runways and trees. These exclusion areas can introduce spatial structure into the baseline distribution that enhance the PSF sidelobes and reduce the angular dynamic range. In this paper we present a new method of constrained antenna placement that reduces the spatial structure in the baseline distribution. This method not only outperforms random placement algorithms that avoid exclusion zones, but surprisingly outperforms random placement algorithms without constraints to provide what we believe are the smoothest constrained baseline distributions developed to date. We use our new algorithm to determine antenna placements for the originally planned MWA, and present the antenna locations, baseline distribution, and snapshot PSF for this array choice.
Published: 2012

99. Subtraction of point sources from interferometric radio images through an algebraic forward modelling scheme

Author: Stephen M. Ord, Daniel A. Mitchell, Gianni Bernardi, B. Pindor, L. J. Greenhill, J. S. B. Wyithe, and Randall B. Wayth
Subjects: Physics, Observational error, 010308 nuclear & particles physics, Dynamic range, Astrophysics::Instrumentation and Methods for Astrophysics, Subtraction, Astronomy and Astrophysics, Astrophysics, Residual, 01 natural sciences, Interferometry, Orders of magnitude (time), Space and Planetary Science, 0103 physical sciences, Deconvolution, 010303 astronomy & astrophysics, Reionization, Algorithm
Abstract: We present a method for subtracting point sources from interferometric radio images via forward modeling of the instrument response and involving an algebraic nonlinear minimization. The method is applied to simulated maps of the Murchison Wide-field Array but is generally useful in cases where only image data are available. After source subtraction, the residual maps have no statistical difference to the expected thermal noise distribution at all angular scales, indicating high effectiveness in the subtraction. Simulations indicate that the errors in recovering the source parameters decrease with increasing signal-to-noise ratio, which is consistent with the theoretical measurement errors. In applying the technique to simulated snapshot observations with the Murchison Wide-field Array, we found that all 101 sources present in the simulation were recovered with an average position error of 10 arcsec and an average flux density error of 0.15%. This led to a dynamic range increase of approximately 3 orders of magnitude. Since all the sources were deconvolved jointly, the subtraction was not limited by source sidelobes but by thermal noise. This technique is a promising deconvolution method for upcoming radio arrays with a huge number of elements, and a candidate for the difficult task of subtracting foreground sources from observations of the 21 cm neutral Hydrogen signal from the epoch of reionization.
Published: 2011

100. Characterizing Signal Loss in the 21 cm Reionization Power Spectrum: A Revised Study of PAPER-64

Author: Jonathan C. Pober, Chris Carilli, Joshua S. Dillon, David MacMahon, Daniel C. Jacobs, Adrian Liu, Chuneeta D. Nunhokee, Aaron R. Parsons, Gianni Bernardi, Pat Klima, Richard F. Bradley, Matthew Kolopanis, Matthew R. Dexter, David DeBoer, Zaki S. Ali, Carina Cheng, Saul A. Kohn, James E. Aguirre, David F. Moore, William P. Walbrugh, Andre Walker, and USA
Subjects: Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010308 nuclear & particles physics, media_common.quotation_subject, FOS: Physical sciences, Spectral density, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Galaxy, Universe, Statistical power, Precision Array for Probing the Epoch of Reionization, Stars, Space and Planetary Science, 0103 physical sciences, Dark Ages, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Reionization, Astrophysics - Cosmology and Nongalactic Astrophysics, media_common
Abstract: The Epoch of Reionization (EoR) is an uncharted era in our Universe's history during which the birth of the first stars and galaxies led to the ionization of neutral hydrogen in the intergalactic medium. There are many experiments investigating the EoR by tracing the 21cm line of neutral hydrogen. Because this signal is very faint and difficult to isolate, it is crucial to develop analysis techniques that maximize sensitivity and suppress contaminants in data. It is also imperative to understand the trade-offs between different analysis methods and their effects on power spectrum estimates. Specifically, with a statistical power spectrum detection in HERA's foreseeable future, it has become increasingly important to understand how certain analysis choices can lead to the loss of the EoR signal. In this paper, we focus on signal loss associated with power spectrum estimation. We describe the origin of this loss using both toy models and data taken by the 64-element configuration of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER). In particular, we highlight how detailed investigations of signal loss have led to a revised, higher 21cm power spectrum upper limit from PAPER-64. Additionally, we summarize errors associated with power spectrum error estimation that were previously unaccounted for. We focus on a subset of PAPER-64 data in this paper; revised power spectrum limits from the PAPER experiment are presented in a forthcoming paper by Kolopanis et al. (in prep.) and supersede results from previously published PAPER analyses., 25 pages, 18 figures, Accepted by ApJ
Published: 2018

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