Author: "R. C. Vermeulen" - Searchworks@Jio Institute Digital Library Search Results

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84 results on '"R. C. Vermeulen"'

1. P1274: EARLY DETECTION OF NON-HODGKIN LYMPHOMA IN PREDISPOSED PATIENT GROUPS THROUGH IMMUNOGENETIC SEQUENCING

Author: P. M. Kolijn, K. Boer, O. C. Manintveld, C. C. Baan, P. L. van Daele, M. A. Versnel, R. C. Vermeulen, and A. W. Langerak
Subjects: Diseases of the blood and blood-forming organs, RC633-647.5
Published: 2022
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2. Detection statistics of the RadioAstron AGN survey

Author: Jamie McCallum, A. S. Andrianov, J. R. Rizzo, M. S. Burgin, C. García-Miró, Paweł Wolak, E. V. Kravchenko, Yu. A. Kovalev, M. V. Shatskaya, Tuomas Savolainen, James M. Anderson, Alexander B. Pushkarev, A. V. Kovalenko, G. Giovannini, N. N. Shakhvorostova, Marcello Giroletti, A. M. Kutkin, I. A. Rakhimov, Mikhail M. Lisakov, V. I. Kostenko, Norbert Bartel, Sándor Frey, I. N. Pashchenko, Magdalena Kunert-Bajraszewska, Zhi-Qiang Shen, Tapasi Ghosh, D. G. Nair, P. de Vicente, Ivan Litovchenko, Kirill Sokolovsky, J. A. Zensus, Philip G. Edwards, Antonis Polatidis, Shinji Horiuchi, Anastasios Melis, V. A. Zuga, Frank D. Ghigo, Jun Yi Koay, Tao An, P. A. Voitsik, S. F. Likhachev, J. F. H. Quick, I. A. Girin, Marcin P. Gawronski, David L. Jauncey, M. A. Kharinov, C. S. Reynolds, A. E. Melnikov, N. S. Kardashev, Simon Ellingsen, V. Yu. Avdeev, Hayley Bignall, D. V. Ivanov, R. C. Vermeulen, Leonid I. Gurvits, Chris Phillips, Yuri Y. Kovalev, M. A. Shchurov, Alexey Rudnitskiy, Carlo Migoni, Department of Electronics and Nanoengineering, Aalto-yliopisto, and Aalto University
Subjects: Atmospheric Science, Brightness, Active galactic nucleus, 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, Science program, FOS: Physical sciences, Aerospace Engineering, Astrophysics::Cosmology and Extragalactic Astrophysics, galaxies [Radio continuum], 01 natural sciences, 0103 physical sciences, Statistics, Very-long-baseline interferometry, Space VLBI, 010303 astronomy & astrophysics, Quasars, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Active galactic nuclei, Astronomy and Astrophysics, Quasar, Astrophysics - Astrophysics of Galaxies, Geophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), General Earth and Planetary Sciences, jets [Galaxies], Astrophysics - High Energy Astrophysical Phenomena
Abstract: The largest Key Science Program of the RadioAstron space VLBI mission is a survey of active galactic nuclei (AGN). The main goal of the survey is to measure and study the brightness of AGN cores in order to better understand the physics of their emission while taking interstellar scattering into consideration. In this paper we present detection statistics for observations on ground-space baselines of a complete sample of radio-strong AGN at the wavelengths of 18, 6, and 1.3 cm. Two-thirds of them are indeed detected by RadioAstron and are found to contain extremely compact, tens to hundreds of $\mu$as structures within their cores., Comment: Accepted to the Advances in Space Research special issue "High-resolution Space-Borne Radio Astronomy"
Published: 2020

3. A large light-mass component of cosmic rays at 10(17)-10(17.5) electronvolts from radio observations

Author: Vishambhar Pandey, D. D. Mulcahy, M. A. Garrett, J. van Leeuwen, Tim Hassall, Adam Deller, Harvey Butcher, D. Engels, H. Paas, John Conway, J. E. Enriquez, A. I. F. Stewart, M. Pandey-Pommier, Matthias Steinmetz, Rob Fender, B. Ciardi, M. Pietka, E. Juette, G. van Diepen, P. N. Best, M. C. Toribio, A. Horneffer, Chiara Ferrari, M. P. van Haarlem, S. Duscha, Mark J. Bentum, Stefan J. Wijnholds, Jochen Eislöffel, Sarod Yatawatta, Emanuela Orrú, M. Kuniyoshi, Michael Kramer, Anna Nelles, C. Vogt, R. J. van Weeren, Martin Bell, Maaijke Mevius, John D. Swinbank, P. Maat, Matthias Hoeft, M. J. Norden, Pim Schellart, D. McKay-Bukowski, J. A. Zensus, John McKean, Dominik J. Schwarz, Richard Fallows, Aris Karastergiou, Ph. Zarka, V. I. Kondratiev, T. N. G. Trinh, Stijn Buitink, Heino Falcke, Michael W. Wise, Jörg P. Rachen, Benjamin Stappers, Jason W. T. Hessels, J. Sluman, Gianni Bernardi, Jörg R. Hörandel, I. M. Avruch, James M. Anderson, F. de Gasperin, Frank Breitling, Roberto Pizzo, H. J. A. Röttgering, Satyendra Thoudam, G. Kuper, Olaf Wucknitz, M. Serylak, H. Munk, Wilfred Frieswijk, Ashish Asgekar, Marcus Brüggen, M. Iacobelli, Y. Tang, W. Reich, S. ter Veen, A. W. Gunst, Anna M. M. Scaife, Laura Rossetto, Ralph A. M. J. Wijers, A. G. Polatidis, Rebecca McFadden, Arthur Corstanje, Annalisa Bonafede, Christian Vocks, G. M. Loose, Sera Markoff, Jean-Mathias Grießmeier, Michel Tagger, D. Carbone, R. C. Vermeulen, T. Huege, Olaf Scholten, Oleg Smirnov, Huib Intema, Cyril Tasse, J. W. Broderick, E. de Geus, R. J. Dettmar, George Heald, W. N. Brouw, Gottfried Mann, High Energy Astrophys. & Astropart. Phys (API, FNWI), Radboud University [Nijmegen], Netherlands Institute for Radio Astronomy (ASTRON), Karlsruhe Institute of Technology (KIT), University of Groningen [Groningen], Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Laboratoire Analyse, Géométrie et Applications (LAGA), Université Paris 8 Vincennes-Saint-Denis (UP8)-Université Paris 13 (UP13)-Institut Galilée-Centre National de la Recherche Scientifique (CNRS), Institute for Mathematics Applied to Geoscience, National Center for Atmospheric Research [Boulder] (NCAR), SRON Netherlands Institute for Space Research (SRON), Australia Telescope National Facility (ATNF), Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), University of Edinburgh, Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), University of Southampton, Kapteyn Astronomical Institute [Groningen], University of Amsterdam [Amsterdam] (UvA), 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], Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Medstar Research Institute, Astronomisches Institut der Ruhr-Universität Bochum, Ruhr-Universität Bochum [Bochum], Thüringer Landessternwarte Tautenburg (TLS), SETI Institute, Institute of Mathematical and Physical Sciences, Département de Géologie, Université de Montréal (UdeM), Leiden Observatory [Leiden], Universiteit Leiden, 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), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Max-Planck-Institut für Radioastronomie (MPIFR), Oxford Astrophysics, University of Oxford, Columbia Astrophysics Laboratory (CAL), Columbia University [New York], 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), 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), 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], Université Paris-Sud - Paris 11 (UP11), SKA South Africa, Ska South Africa, Galaxies, Etoiles, Physique, Instrumentation (GEPI), 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), Finca El Encin, Instituto Madrileño de Investigación y Desarrollo Rural, Agrario y Alimentario (IMIDRA), Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, Observatoire de Paris - Site de Paris (OP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), 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, European Project: 227610,EC:FP7:ERC,ERC-2008-AdG,LOFAR-AUGER(2009), European Project: 640130,H2020,ERC-2014-STG,LOFAR(2015), Radboud university [Nijmegen], Institute for Nuclear Physics (IKP), Karlsruhe Institute of Technology, nstitute for Nuclear Physics (IKP), Karlsruhe Institute of Technology, Université Paris 8 Vincennes-Saint-Denis (UP8)-Centre National de la Recherche Scientifique (CNRS)-Institut Galilée-Université Paris 13 (UP13), 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), Research unit Astroparticle Physics, Astronomy, and Kapteyn Astronomical Institute
Subjects: TELESCOPE, High-energy astronomy, Astronomy, Astrophysics::High Energy Astrophysical Phenomena, Cosmic ray, Astrophysics, Electron, Astrophysics::Cosmology and Extragalactic Astrophysics, Radiation, EXTENSIVE AIR-SHOWERS, 01 natural sciences, 0103 physical sciences, 010303 astronomy & astrophysics, Astroparticle physics, Physics, Multidisciplinary, COSMIC cancer database, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, LOFAR, ENERGY-SPECTRUM, SIMULATIONS, PULSES, High-energy astrophysics, Air shower, 13. Climate action, [SDU]Sciences of the Universe [physics], ARRAY, Neutrino, Particle astrophysics, EMISSION
Abstract: Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 1017–1018 electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal1 comes from accelerators capable of producing cosmic rays of these energies2. Cosmic rays initiate air showers—cascades of secondary particles in the atmosphere—and their masses can be inferred from measurements of the atmospheric depth of the shower maximum3 (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground4. Current measurements5 have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays6,7,8 is a rapidly developing technique9 for determining Xmax (refs 10, 11) with a duty cycle of, in principle, nearly 100 per cent. The radiation is generated by the separation of relativistic electrons and positrons in the geomagnetic field and a negative charge excess in the shower front6,12. Here we report radio measurements of Xmax with a mean uncertainty of 16 grams per square centimetre for air showers initiated by cosmic rays with energies of 1017–1017.5 electronvolts. This high resolution in Xmax enables us to determine the mass spectrum of the cosmic rays: we find a mixed composition, with a light-mass fraction (protons and helium nuclei) of about 80 per cent. Unless, contrary to current expectations, the extragalactic component of cosmic rays contributes substantially to the total flux below 1017.5 electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 1017–1017.5 electronvolt range.
Published: 2019

4. The LOFAR Two-metre Sky Survey. II. First data release

Author: Eskil Varenius, Huub Röttgering, Magdalena Kunert-Bajraszewska, Ricardo Genova-Santos, Judith H. Croston, D. Nisbet, R. Lakhoo, R. Kondapally, F. Savini, Joseph R. Callingham, A. O. Clarke, H. R. Stacey, M. H. D. van der Wiel, Isabella Prandoni, Antonia Rowlinson, R. Pizzo, Gianfranco Brunetti, David Bacon, George K. Miley, Marcus Brüggen, L. Alegre, R.-J. Dettmar, C. Dumba, R. J. van Weeren, Volker Heesen, Stephen Bourke, G. Calistro Rivera, A. Botteon, J. Sabater, M. Mirmont, G. Gürkan, Andrea Merloni, Torsten A. Enßlin, Marek Jamrozy, Philip Best, A. Drabent, Marcellin Atemkeng, Glenn J. White, R. C. Vermeulen, Wolfgang Reich, Neal Jackson, Chiara Ferrari, Marco Iacobelli, Huib Intema, J. B. R. Oonk, D. N. Hoang, John Conway, A. Wilber, Marisa Brienza, T. J. Dijkema, B. Webster, M. A. Garrett, Simon Perkins, A. P. Mechev, Shane O'Sullivan, Christopher J. Conselice, I. van Bemmel, Annalisa Bonafede, Oleg Smirnov, John L. Quinn, John McKean, G. Kokotanekov, Subhash C. Mandal, Daniel J. Smith, C. L. Hale, Arti Goyal, Błażej Nikiel-Wroczyński, K. L. Emig, S. Urquhart, Marijke Haverkorn, Timothy W. Shimwell, R. Morganti, Michael W. Wise, Elizabeth K. Mahony, Beatriz Mingo, Arpad Miskolczi, C. A. Jackson, Leah K. Morabito, D. A. Rafferty, A. Saxena, C. Roskowinski, Rachel Cochrane, C. Schrijvers, M. Mevius, Wendy L. Williams, E. Bonnassieux, Rossella Cassano, Matthias Hoeft, Krzysztof T. Chyzy, Dominik J. Schwarz, B. Hugo, Robert Beswick, George Heald, C. Tasse, S. Mooney, Jeremy J. Harwood, Emanuela Orru, Martin J. Hardcastle, Kenneth Duncan, S. S. Sridhar, Cathy Horellou, Matt J. Jarvis, L. Bester, F. de Gasperin, Aleksandar Shulevski, A. Danezi, V. H. Mahatma, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), 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), Astronomy, 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 Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), 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, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Shimwell T.W., Tasse C., Hardcastle M.J., Mechev A.P., Williams W.L., Best P.N., Rottgering H.J.A., Callingham J.R., Dijkema T.J., De Gasperin F., Hoang D.N., Hugo B., Mirmont M., Oonk J.B.R., Prandoni I., Rafferty D., Sabater J., Smirnov O., Van Weeren R.J., White G.J., Atemkeng M., Bester L., Bonnassieux E., Bruggen M., Brunetti G., Chy K.T., Cochrane R., Conway J.E., Croston J.H., Danezi A., Duncan K., Haverkorn M., Heald G.H., Iacobelli M., Intema H.T., Jackson N., Jamrozy M., Jarvis M.J., Lakhoo R., Mevius M., Miley G.K., Morabito L., Morganti R., Nisbet D., Orru E., Perkins S., Pizzo R.F., Schrijvers C., Smith D.J.B., Vermeulen R., Wise M.W., Alegre L., Bacon D.J., Van Bemmel I.M., Beswick R.J., Bonafede A., Botteon A., Bourke S., Brienza M., Calistro Rivera G., Cassano R., Clarke A.O., Conselice C.J., Dettmar R.J., Drabent A., Dumba C., Emig K.L., Ensslin T.A., Ferrari C., Garrett M.A., Genova-Santos R.T., Goyal A., Gurkan G., Hale C., Harwood J.J., Heesen V., Hoeft M., Horellou C., Jackson C., Kokotanekov G., Kondapally R., Kunert-Bajraszewska M., Mahatma V., Mahony E.K., Mandal S., McKean J.P., Merloni A., Mingo B., Miskolczi A., Mooney S., Nikiel-Wroczynski B., O'Sullivan S.P., Quinn J., Reich W., Roskowinski C., Rowlinson A., Savini F., Saxena A., Schwarz D.J., Shulevski A., Sridhar S.S., Stacey H.R., Urquhart S., Van Der Wiel M.H.D., Varenius E., Webster B., and Wilber A.
Subjects: Astronomy, radio continuum: general, Flux, techniques: image processing, Astrophysics, 01 natural sciences, CLUSTER ENVIRONMENTS, ST/M001229/1, Survey, 010303 astronomy & astrophysics, SOUTHERN SKY, media_common, astro-ph.HE, Physics, CALIBRATION, High Energy Astrophysical Phenomena (astro-ph.HE), image processing [techniques], UNDERSTANDING RADIO POLARIMETRY, ST/R00109X/1, ST/P000096/1, astro-ph.CO, general [radio continuum], Catalog, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Noise (radio), Astrophysics - Cosmology and Nongalactic Astrophysics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), astro-ph.GA, media_common.quotation_subject, FOS: Physical sciences, Declination, surveys, 0103 physical sciences, [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], AGN, Instrumentation and Methods for Astrophysics (astro-ph.IM), STFC, ST/M001326/1, 010308 nuclear & particles physics, RCUK, Astronomy and Astrophysics, LOFAR, Astrophysics - Astrophysics of Galaxies, Galaxy, Redshift, GALAXY, ST/M001008/1, Space and Planetary Science, Sky, IMAGING SURVEY, DISCOVERY, Astrophysics of Galaxies (astro-ph.GA), FLUX-DENSITY SCALE, Right ascension, EMISSION, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], catalogs, astro-ph.IM
Abstract: The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120-168MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this data release 424 square degrees, or 2% of the eventual coverage, in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45$^\circ$00$'$00$''$ to 57$^\circ$00$'$00$''$) were mapped using a fully automated direction-dependent calibration and imaging pipeline that we developed. A total of 325,694 sources are detected with a signal of at least five times the noise, and the source density is a factor of $\sim 10$ higher than the most sensitive existing very wide-area radio-continuum surveys. The median sensitivity is S$_{\rm 144 MHz} = 71\,\mu$Jy beam$^{-1}$ and the point-source completeness is 90% at an integrated flux density of 0.45mJy. The resolution of the images is 6$''$ and the positional accuracy is within 0.2$''$. This data release consists of a catalogue containing location, flux, and shape estimates together with 58 mosaic images that cover the catalogued area. In this paper we provide an overview of the data release with a focus on the processing of the LOFAR data and the characteristics of the resulting images. In two accompanying papers we provide the radio source associations and deblending and, where possible, the optical identifications of the radio sources together with the photometric redshifts and properties of the host galaxies. These data release papers are published together with a further $\sim$20 articles that highlight the scientific potential of LoTSS., Comment: 16 figures, 1 table and 22 pages. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal
Published: 2019

5. The association of a J-burst with a solar jet

Author: Helmut O. Rucker, Rebecca McFadden, B. Ciardi, J. M. Anderson, H. Munk, J. W. Broderick, O. Wucknitz, H. Paas, E. Juette, W. Reich, Heino Falcke, Matthias Hoeft, Hamish A. S. Reid, Oleg Smirnov, L. Cerrigone, A. G. Polatidis, Philip Best, Emanuela Orrú, Matthias Steinmetz, J. Magdalenic, D. D. Mulcahy, Gottfried Mann, C. Vocks, P. Zarka, V. N. Pandey, Ashish Asgekar, Mark J. Bentum, Gerard H. Kuper, A. Nelles, Annalisa Bonafede, M. Iacobelli, Diana E. Morosan, Dominik J. Schwarz, M. Pandey-Pommier, M. C. Toribio, R. C. Vermeulen, Jochen Eislöffel, Jean-Mathias Griessmeier, M. Tagger, S. ter Veen, A. W. Gunst, S. Duscha, Mario M. Bisi, R. Blaauw, R. J. van Weeren, D. McKay-Bukowski, I. M. Avruch, Peter T. Gallagher, John McKean, Martin Bell, E. de Geus, M. A. Garrett, Richard Fallows, Frank Breitling, Bo Thidé, J. Sluman, Roberto Pizzo, Marcus Brüggen, Satyendra Thoudam, Astronomy, Kapteyn Astronomical Institute, Trinity College Dublin, Netherlands Institute for Radio Astronomy (ASTRON), SUPA School of Physics and Astronomy [Glasgow], University of Glasgow, Leibniz-Institut für Astrophysik Potsdam (AIP), STFC Rutherford Appleton Laboratory (RAL), Science and Technology Facilities Council (STFC), Royal Observatory of Belgium [Brussels] (ROB), Austrian Academy of Sciences (OeAW), Swedish Institute of Space Physics [Uppsala] (IRF), GeoForschungsZentrum - Helmholtz-Zentrum Potsdam (GFZ), Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Royal Observatory Edinburgh (ROE), University of Edinburgh, Jacobs University [Bremen], Universität Hamburg (UHH), Max-Planck-Institut für Astrophysik (MPA), Max-Planck-Gesellschaft, Thüringer Landessternwarte Tautenburg (TLS), 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), Leiden Observatory [Leiden], Universiteit Leiden, Ruhr-Universität Bochum [Bochum], University of Oulu, Radboud University [Nijmegen], 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), Max-Planck-Institut für Radioastronomie (MPIFR), Universität Bielefeld, Rhodes University, Grahamstown, Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, 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), 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), Universiteit Leiden [Leiden], Radboud university [Nijmegen], 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 Harvard University [Cambridge]-Smithsonian Institution
Subjects: corona [Sun], 010504 meteorology & atmospheric sciences, Astronomy, particle emission [Sun], Astrophysics, 01 natural sciences, ELECTRON-BEAMS, CORONA, Sun: magnetic, Coronal mass ejection, Astrophysics::Solar and Stellar Astrophysics, GeneralLiterature_REFERENCE(e.g.,dictionaries,encyclopedias,glossaries), 010303 astronomy & astrophysics, Sun: magnetic fields, fields, Physics, Jet (fluid), Solar flare, Sun: radio radiation, Astrophysics::Instrumentation and Methods for Astrophysics, FLARE, Astrophysics - Solar and Stellar Astrophysics, magnetic fields [Sun], Physical Sciences, Physics::Space Physics, Astrophysics::Earth and Planetary Astrophysics, FLUX, DYNAMICS-OBSERVATORY SDO, Field line, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy & Astrophysics, ACCELERATION, Computer Science::Digital Libraries, III BURSTS, Sun: particle emission, 0103 physical sciences, Solar and Stellar Astrophysics (astro-ph.SR), 0105 earth and related environmental sciences, Science & Technology, radio radiation [Sun], [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Sun: corona, Northern Hemisphere, Astronomy and Astrophysics, Magnetic reconnection, LOFAR, Physics::History of Physics, X-RAY JETS, 13. Climate action, Space and Planetary Science, Extreme ultraviolet, RADIO-EMISSION
Abstract: Context. The Sun is an active star that produces large-scale energetic events such as solar flares and coronal mass ejections and numerous smaller-scale events such as solar jets. These events are often associated with accelerated particles that can cause emission at radio wavelengths. The reconfiguration of the solar magnetic field in the corona is believed to be the cause of the majority of solar energetic events and accelerated particles. Aims. Here, we investigate a bright J-burst that was associated with a solar jet and the possible emission mechanism causing these two phenomena. Methods. We used data from the Solar Dynamics Observatory (SDO) to observe a solar jet, and radio data from the Low Frequency Array (LOFAR) and the Nan\c{c}ay Radioheliograph (NRH) to observe a J-burst over a broad frequency range (33-173 MHz) on 9 July 2013 at ~11:06 UT. Results. The J-burst showed fundamental and harmonic components and it was associated with a solar jet observed at extreme ultraviolet wavelengths with SDO. The solar jet occurred at a time and location coincident with the radio burst, in the northern hemisphere, and not inside a group of complex active regions in the southern hemisphere. The jet occurred in the negative polarity region of an area of bipolar plage. Newly emerged positive flux in this region appeared to be the trigger of the jet. Conclusions. Magnetic reconnection between the overlying coronal field lines and the newly emerged positive field lines is most likely the cause of the solar jet. Radio imaging provides a clear association between the jet and the J-burst which shows the path of the accelerated electrons., Comment: 11 pages, 8 figures
Published: 2017

6. 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

7. 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

8. 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

9. Imaging Jupiter's radiation belts down to 127 MHz with LOFAR

Author: Gianni Bernardi, Jörg R. Hörandel, A. G. Polatidis, Ashish Asgekar, A. Nelles, Angélica Sicard, H. Munk, R. J. van Weeren, Jason W. T. Hessels, D. McKay-Bukowski, I. de Pater, Matthias Hoeft, Oleg Smirnov, A. W. Gunst, Frank Breitling, Arthur Corstanje, Sebastien Hess, Quentin Nénon, Mark J. Bentum, J. van Leeuwen, R. C. Vermeulen, M. Loose, P. Zarka, H. J. A. Röttgering, P. Maat, M. J. Norden, M. Tagger, J. Moldón, F. de Gasperin, S. Bourdarie, Rene P. Breton, Annalisa Bonafede, John D. Swinbank, I. van Bemmel, Stephane Corbel, Martin Bell, V. I. Kondratiev, M. Pandey-Pommier, M. Iacobelli, James M. Anderson, Roberto Pizzo, Marcus Brüggen, Satyendra Thoudam, M. C. Toribio, Gerard H. Kuper, Antonia Rowlinson, Jochen Eislöffel, S. Duscha, Rebecca McFadden, M. A. Garrett, Daniel Santos-Costa, Julien N. Girard, Matthias Steinmetz, B. Ciardi, O. Wucknitz, J.-M. Grießmeier, M. Kuniyoshi, Ralph A. M. J. Wijers, Wilfred Frieswijk, Heino Falcke, C. Tasse, W. N. Brouw, S. Markov, Emanuela Orrú, H. Paas, Adam Deller, W. Reich, Dominik J. Schwarz, J. W. Broderick, E. Juette, G. Mann, Philip Best, C. Vocks, E. de Geus, Girard, J.N., Zarka, P., Tasse, C., Hess, S., De Pater, I., Santos-Costa, D., Nenon, Q., Sicard, A., Bourdarie, S., Anderson, J., Asgekar, A., Bell, M.E., Van Bemmel, I., Bentum, M.J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Breton, R.P., Broderick, J.W., Brouw, W.N., Brüggen, M., Ciardi, B., Corbel, S., Corstanje, A., De Gasperin, F., De Geus, E., Deller, A., Duscha, S., Eislöffel, J., Falcke, H., Frieswijk, W., Garrett, M.A., Grießmeier, J., Gunst, A.W., Hessels, J.W.T., Hoeft, M., Hörandel, J., Iacobelli, M., Juette, E., Kondratiev, V.I., Kuniyoshi, M., Kuper, G., Van Leeuwen, J., Loose, M., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Moldon, J., Munk, H., Nelles, A., Norden, M.J., Orru, E., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A.G., Reich, W., Röttgering, H., Rowlinson, A., Schwarz, D., Smirnov, O., Steinmetz, M., Swinbank, J., Tagger, M., Thoudam, S., Toribio, M.C., Vermeulen, R., Vocks, C., Van Weeren, R.J., Wijers, R.A.M.J., Wucknitz, O., 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), 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), Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, ONERA - The French Aerospace Lab [Toulouse], ONERA, Netherlands Institute for Radio Astronomy (ASTRON), University of Southampton, Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE (UMR_7585)), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Royal Observatory Edinburgh (ROE), University of Edinburgh, Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), Jodrell Bank Centre for Astrophysics (JBCA), University of Manchester [Manchester], Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Radboud University [Nijmegen], Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Thüringer Landessternwarte Tautenburg (TLS), Leiden Observatory [Leiden], Universiteit Leiden, Unité Scientifique de la Station de Nançay (USN), Observatoire des Sciences de l'Univers en région Centre (OSUC), 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), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), 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], Max-Planck-Institut für Radioastronomie (MPIFR), University of Oulu, University of Groningen [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), CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Universität Bielefeld, Rhodes University, Grahamstown, Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, ANR-11-IDEX-0005,USPC,Université Sorbonne Paris Cité(2011), European Project: 228261,EC:FP7:ERC,ERC-2008-AdG,SPARSEASTRO(2009), ITA, GBR, FRA, DEU, NLD, 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), 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), 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, 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), PSL Research University (PSL)-PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Jodrell Bank Centre for Astrophysics, Université d'Orléans (UO)-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)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), 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), DPMMS/CMS, University of Cambridge [UK] (CAM), ANR-11-IDEX-0005-02/10-LABX-0023,UnivEarthS,Earth - Planets - Universe: observation, modeling, transfer(2011), Astronomy, High Energy Astrophys. & Astropart. Phys (API, FNWI), and Faculty of Science
Subjects: radio continuum: planetary systems, Brightness, 010504 meteorology & atmospheric sciences, radio continuum: planetary, EWI-27447, Astronomy, Astrophysics::High Energy Astrophysical Phenomena, Magnetosphere, FOS: Physical sciences, Astrophysics, Electron, METIS-321662, 7. Clean energy, 01 natural sciences, Jupiter, symbols.namesake, 0103 physical sciences, Emission spectrum, IR-103183, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 0105 earth and related environmental sciences, Physics, Earth and Planetary Astrophysics (astro-ph.EP), [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Radio continuum: planetary system, Planets and satellites: magnetic field, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, planets and satellites: magnetic fields, Spectral flux density, 13. Climate action, Space and Planetary Science, Van Allen radiation belt, Techniques: interferometric, symbols, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, systems, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Earth and Planetary Astrophysics
Abstract: Context. Observing Jupiter's synchrotron emission from the Earth remains today the sole method to scrutinize the distribution and dynamical behavior of the ultra energetic electrons magnetically trapped around the planet (because in-situ particle data are limited in the inner magnetosphere). Aims. We perform the first resolved and low-frequency imaging of the synchrotron emission with LOFAR at 127 MHz. The radiation comes from low energy electrons (~1-30 MeV) which map a broad region of Jupiter's inner magnetosphere. Methods (see article for complete abstract) Results. The first resolved images of Jupiter's radiation belts at 127-172 MHz are obtained along with total integrated flux densities. They are compared with previous observations at higher frequencies and show a larger extent of the synchrotron emission source (>=4 $R_J$). The asymmetry and the dynamic of east-west emission peaks are measured and the presence of a hot spot at lambda_III=230 {\deg} $\pm$ 25 {\deg}. Spectral flux density measurements are on the low side of previous (unresolved) ones, suggesting a low-frequency turnover and/or time variations of the emission spectrum. Conclusions. LOFAR is a powerful and flexible planetary imager. The observations at 127 MHz depict an extended emission up to ~4-5 planetary radii. The similarities with high frequency results reinforce the conclusion that: i) the magnetic field morphology primarily shapes the brightness distribution of the emission and ii) the radiating electrons are likely radially and latitudinally distributed inside about 2 $R_J$. Nonetheless, the larger extent of the brightness combined with the overall lower flux density, yields new information on Jupiter's electron distribution, that may shed light on the origin and mode of transport of these particles., Comment: 10 pages, 12 figures, accepted for publication in A&A (27/11/2015) - abstract edited because of limited characters
Published: 2015

10. A multi-epoch VLBI survey of the kinematics of CFJ sources

Author: S. Britzen, R. C. Vermeulen, R. M. Campbell, G. B. Taylor, T. J. Pearson, A. C. S. Readhead, W. Xu, I. W. Browne, D. R. Henstock, and P. Wilkinson
Subjects: Physics, education.field_of_study, Superluminal motion, Population, Astronomy and Astrophysics, Quasar, Context (language use), Astrophysics, Kinematics, Luminosity, Acceleration, Space and Planetary Science, Very-long-baseline interferometry, education
Abstract: Context. This is the second of a series of papers presenting VLBI observations of the 293 Caltech-Jodrell Bank Flat-Spectrum (hereafter CJF) sources and their analysis. Aims. To obtain a consistent motion dataset large enough to allow the systematic properties of the population to be studied. Methods. We present the detailed kinematic analysis of the complete fl ux-density limited CJF survey. We computed 2-D kinematic models based on the optimal model-fitting parameters of mult i-epoch VLBA observations. This allows us to calculate not only radial, but also orthogonal motions, and thus to study curvature and acceleration. Statistical tests of the motions measured an d their reliability have been performed. A correlation analysis between the derived apparent motions, luminosities, spectral indices, an d core dominance and the resulting consequences is described. Results. With at least one velocity in each of 237 sources, this sample is much larger than any available before and allows a meaningful statistical investigation of apparent motions and any poss ible correlations with other parameters in AGN jets. The main results to emerge are as follows: - In general motions are not consistent with a single uniform velocity applicable to all components along a jet. - We find a slight trend towards a positive outward accele ration and also adduce some evidence for greater acceleration in the inner-most regions. - We find a lack of fast components at phys ical distances less than a few pc from the reference feature. - Only ∼4% of the components from galaxies and
Published: 2008

11. A multi-epoch VLBI survey of the kinematics of CJF sources

Author: R. C. Vermeulen, A. C. S. Readhead, W. Xu, D. R. Henstock, Ian Browne, Silke Britzen, Robert M. Campbell, T. J. Pearson, P. N. Wilkinson, and G. B. Taylor
Subjects: Physics, Series (stratigraphy), Epoch (reference date), Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Context (language use), Astrophysics, Kinematics, Geodesy, Residual, Space and Planetary Science, Very-long-baseline interferometry, Visibility, Data reduction
Abstract: Context: This is the first of a series of papers presenting VLBI observations of the 293 Caltech-Jodrell Bank Flat-Spectrum (hereafter CJF) sources and their analysis. Aims: One of the major goals of the CJF is to make a statistical study of the apparent velocities of the sources. Methods: We have conducted global VLBI and VLBA observations at 5 GHz since 1990, accumulating thirteen separate observing campaigns. Results: We present here an overview of the observations, give details of the data reduction and present the source parameters resulting from a model-fitting procedure. For every source at every observing epoch, an image is shown, built up by restoring the model-fitted components, convolved with the clean beam, into the residual image, which was made by Fourier transforming the visibility data after first subtracting the model-fitted components in the uv-plane. Overplotted we show symbols to represent the model components. Conclusions: We have produced VLBI images of all but 5 of the 293 sources in the complete CJF sample at several epochs and investigated the kinematics of 266 AGN., Comment: Figure 1 and Table 2 are only available in electronic form at the CDS and soon at http://www.mpifr-bonn.mpg.de/staff/sbritzen/cjf.html
Published: 2007

12. Calibrating the absolute amplitude scale for air showers measured at LOFAR

Author: A. Haungs, Stijn Buitink, A. Nelles, Olaf Scholten, Oleg Smirnov, Pim Schellart, George Heald, Jörg P. Rachen, Jörg R. Hörandel, Maria Krause, A. G. Polatidis, Emanuela Orrú, Wilfred Frieswijk, H. J. A. Röttgering, W. N. Brouw, Rebecca McFadden, Frank G. Schröder, J. Kohler, Katrin Link, R. Krause, P. Zarka, M. Iacobelli, J. Sluman, P. N. Best, P. Maat, M. J. Norden, Roberto Pizzo, Satyendra Thoudam, K. Weidenhaupt, M. P. van Haarlem, M. C. Toribio, Gerard H. Kuper, J. E. Enriquez, A. Horneffer, T. Karskens, Harvey Butcher, F. de Gasperin, J. D. Bregman, S. ter Veen, R. C. Vermeulen, Jochen Eislöffel, Heino Falcke, V. I. Kondratiev, M. Pandey-Pommier, H. Paas, E. Juette, M. Bruüggen, R. Hiller, W. Reich, James M. Anderson, Stefan J. Wijnholds, R. J. van Weeren, Arthur Corstanje, A. Karastergiou, B. Ciardi, Matthias Hoeft, D. McKay-Bukowski, Laura Rossetto, O. Wucknitz, T. N. G. Trinh, S. Duscha, C. Tasse, Martin Bell, M. Serylak, Mark J. Bentum, Tim Huege, J. van Leeuwen, M. Kuniyoshi, Vishambhar Pandey, D. Carbone, Ralph A. M. J. Wijers, Dominik J. Schwarz, Richard Fallows, M. A. Garrett, L. Bähren, Martin Erdmann, Annalisa Bonafede, Physics, Astronomy and Astrophysics Research Group, Elementary Particle Physics, Radboud university [Nijmegen], Institut de Génomique Fonctionnelle de Lyon (IGFL), École normale supérieure - Lyon (ENS Lyon)-Institut National de la Recherche Agronomique (INRA)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Karlsruher Institut für Technologie - Campus Nord, Karlsruher Institut für Technologie - Campus Süd, Netherlands Institute for Radio Astronomy (ASTRON), Department of Astrophysics [Nijmegen], Radboud university [Nijmegen]-Radboud university [Nijmegen], University of Groningen [Groningen], Global Aerospace, Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), Jacobs University [Bremen], Kapteyn Astronomical Institute [Groningen], Research School of Astronomy and Astrophysics [Canberra] (RSAA), Australian National University (ANU), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Thüringer Landessternwarte Tautenburg (TLS), Adran Ffiseg, Prifysgol Cymru Aberystwyth, Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Joint Institute for VLBI in Europe (JIVE ERIC), DPMMS/CMS, University of Cambridge [UK] (CAM), Ruhr-Universität Bochum [Bochum], Oxford Astrophysics, University of Oxford [Oxford], Karlsruhe Institute of Technology (KIT), Max-Planck-Institut für Radioastronomie (MPIFR), University of Oulu, University of Groningen, Groningen, Netherlands, Centre de Recherche Astrophysique de Lyon (CRAL), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon), Department of Physics and Astronomy [South Africa], University of the Western Cape, 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), Aucun, Stichting WBBS, Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut National de la Recherche Agronomique (INRA)-École normale supérieure - Lyon (ENS Lyon), 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), 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), 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), Radboud University [Nijmegen], École normale supérieure de Lyon (ENS de Lyon)-Institut National de la Recherche Agronomique (INRA)-Université Claude Bernard Lyon 1 (UCBL), Radboud University [Nijmegen]-Radboud University [Nijmegen], Universiteit Leiden, University of Oxford, 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), University of the Western Cape (UWC), High Energy Astrophys. & Astropart. Phys (API, FNWI), Research unit Astroparticle Physics, Astronomy, and Kapteyn Astronomical Institute
Subjects: Astronomy, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Cosmic ray, Astrophysics::Cosmology and Extragalactic Astrophysics, Optics, Calibration, ddc:610, Instrumentation and Methods for Astrophysics (astro-ph.IM), Instrumentation, Absolute scale, ComputingMilieux_MISCELLANEOUS, Mathematical Physics, High Energy Astrophysical Phenomena (astro-ph.HE), [PHYS]Physics [physics], Physics, business.industry, Astrophysics::Instrumentation and Methods for Astrophysics, LOFAR, Amplitude, Air shower, Experimental High Energy Physics, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Antennas, Radio frequency, Antenna (radio), Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], business
Abstract: Air showers induced by cosmic rays create nanosecond pulses detectable at radio frequencies. These pulses have been measured successfully in the past few years at the LOw Frequency ARray (LOFAR) and are used to study the properties of cosmic rays. For a complete understanding of this phenomenon and the underlying physical processes, an absolute calibration of the detecting antenna system is needed. We present three approaches that were used to check and improve the antenna model of LOFAR and to provide an absolute calibration of the whole system for air shower measurements. Two methods are based on calibrated reference sources and one on a calibration approach using the diffuse radio emission of the Galaxy, optimized for short data-sets. An accuracy of 19% in amplitude is reached. The absolute calibration is also compared to predictions from air shower simulations. These results are used to set an absolute energy scale for air shower measurements and can be used as a basis for an absolute scale for the measurement of astronomical transients with LOFAR., Comment: 34 pages, 10 figures
Published: 2015

13. Optical Spectrophotometry of a Complete Sample of 3CR Lobe-dominated Quasars

Author: L. H. Yu, C. E. Aars, P. J. Beyer, R. C. Vermeulen, D. H. Hough, J. P. Linick, and A. C. S. Readhead
Subjects: Physics, Supermassive black hole, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics, Luminosity, law.invention, Telescope, Space and Planetary Science, Observatory, law, Emission spectrum, Spectrograph, Line (formation)
Abstract: We present results from optical spectrophotometry of 19 of the 25 lobe-dominated quasars in the 3CR complete sample. The optical spectra were obtained with the Hale 5 m telescope at Palomar Observatory, using the blue and red CCDs of the Double Spectrograph, between 1984 and 1992. Additional data from the literature allow us to analyze broad UV/optical emission lines in all 25 objects (100% completeness), with a total of 191 broad-line measurements (far more than the 68 points in the preliminary results presented in the 2002 work of Hough et al.). We examine correlations between the widths of the broad emission lines and several radio-based orientation indicators. These include three measures involving the beamed radio emission on the parsec scale: (1) the prominence of the radio nucleus R, defined as the rest-frame ratio of the nuclear to extended flux density at 5 GHz; (2) an alternate measure of relative strength of the radio nucleus RV, defined as the rest-frame ratio of the 5 GHz radio core luminosity to the optical V-band luminosity; and (3) a pseudoangle θpseudo, derived from a rank ordering of sources based on both R and projected linear size L. An additional orientation indicator based on kiloparsec-scale radio emission was also used: the prominence of the straight, inner Very Large Array jets (Fj), defined as the rest-frame ratio of the jet to jet-lobe flux density at 5 GHz. We confirm earlier studies demonstrating a strong anticorrelation between R and the FWHM of the Mg II λ2798 line; the FWHM also anticorrelates with RV and θpseudo. However, the anticorrelation between R and the FWHM of the C III] λ1909 line originally reported for only 12 objects in the 2002 work of Hough et al. is not seen in the complete sample. To make separate investigations of lines that may originate in two physically distinct regions—the intermediate-line region (ILR) and the very broad line region (VBLR)—we scaled the FWHM measurements to a common mean and standard deviation for each region. The scaled FWHM of ILR lines (C III] λ1909, Mg II λ2798, and Hβ λ4861) anticorrelates with R, RV, and θpseudo, but the FWHM of the VBLR lines (Lyα λ1216, N V λ1240, C IV λ1549, and He II λ1640) shows no evidence of any correlations with these three orientation indicators. These results are consistent with models that divide the broad-line region surrounding the central supermassive black hole into an inner, spherical, high-ionization VBLR and an outer, disklike, low-ionization ILR. These results are also consistent with the unification of core- and lobe-dominated quasars. Simple models fit the log R versus Mg II λ2798 FWHM relationship without unbeamed radio emission or turbulent broad-line cloud velocities; small unbeamed and turbulent components offer slight improvements to the fits, but large contributions are ruled out and the best-fitting range of orientation angles is only mildly restricted (~10°–80°). Some surprising results are anticorrelations between the C IV λ1549 and scaled VBLR line widths and log Fj. The explanation for these anticorrelations—and the lack thereof for the main ILR lines—is not obvious but may be related to weaker beaming in the kiloparsec-scale jets.
Published: 2005

14. The presence and distribution of H I absorbing gas in sub-galactic sized radio sources

Author: Y.M. Pihlstroem, John Conway, and R. C. Vermeulen
Subjects: Physics, business.industry, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Power law, Galaxy, Distribution (mathematics), Space and Planetary Science, Global Positioning System, business, Absorption (electromagnetic radiation), Astrophysics::Galaxy Astrophysics, Order of magnitude, Equipartition theorem, Incidence (geometry)
Abstract: We consider the incidence of HI absorption in intrinsically small sub-galactic sized extragalactic sources selected from sources classified as Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources. We find that the smaller sources (0.5 kpc). Both a spherical and an axi-symmetric gas distribution, with a radial power law density profile, can be used to explain this anti-correlation between projected linear size and HI column density. Since most detections occur in objects classified as galaxies, we argue that if the unified schemes apply to GPS/CSSs a disk distribution for the HI is more likely. The most favoured explanation for the compact sizes of the GPS/CSSs is that they are young sources evolving in a power law density medium. For the GPSs with measured expansion velocities, our derived densities are within an order of magnitude of those estimated from ram-pressure confinement of the lobes assuming equipartition. Our results therefore support the youth model., 12 pages, 8 figures, accepted for publication in A&A
Published: 2003

15. Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei. II. Additional Sources

Author: K. I. Kellermann, J. A. Zensus, R. C. Vermeulen, Matthias Kadler, Eduardo Ros, and Marshall H. Cohen
Subjects: Physics, Brightness, Active galactic nucleus, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Lambda, Sample (graphics), Redshift, Intrinsic brightness, Space and Planetary Science, Very Long Baseline Array
Abstract: We report further results from our imaging survey at 15GHz (lambda=2 cm) with the Very Long Baseline Array. This paper presents single epoch images for 39 sources, bringing the total number of objects in the sample to 171. Our sample is representative of a complete unbiased sample and it will be used for statistical analysis of source properties. We compare the observed brightness temperatures derived from our VLBA observations to those derived from total intensity variations at 22 and 37 GHz. These are consistent with intrinsic brightness temperatures in the range 10^10 to 10^12 K. We also present three new spectroscopic redshift values: z=0.517+/-0.001 for 0026+346, z=1.591+/-0.003 for 0727-115, and z=0.2016+/-0.0004 for 1155+251. Images from this VLBA 2 cm survey are available on the Internet under http://www.cv.nrao.edu/2cmsurvey., 21 pages, 6 figures, 4 tables, 1 appendix. Accepted for publication (August 2002 issue) at The Astronomical Journal. Needs aastex.cls, amsfonts.sty, amssymb.sty, apj.bst, natbib.sty
Published: 2002

16. Parsec-Scale Radio Structure and Broad Optical Emission Lines in a Complete Sample of 3CR Lobe-dominated Quasars

Author: R. C. Vermeulen, L. L. Cross, L. H. Yu, E. M. Phifer, A. C. S. Readhead, D. H. Hough, P. J. Beyer, and E. L. Barth
Subjects: Physics, Jet (fluid), Supermassive black hole, Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Solar prominence, Relativistic beaming, Astrophysical jet, Space and Planetary Science, Very-long-baseline interferometry, Astrophysics::Galaxy Astrophysics
Abstract: We present results from VLBI observations of 24 of the 25 lobe-dominated quasars (LDQs) in the 3CR complete sample and from optical spectrophotometry of 14 of these objects. The VLBI observations were made with a variety of arrays—most recently the Very Long Baseline Array—at frequencies ranging from 5 to 22 GHz during the period 1981–1997. The optical spectra were obtained with the Hale 200 inch (5 m) telescope at Palomar Observatory, using the blue and red CCDs of the Double Spectrograph, between 1984 and 1992. The radio nuclei range in strength over nearly 3 orders of magnitude, from ~0.9 Jy down to ~3 mJy, and were imaged at typical resolutions of ~0.5–1.0 mas and sensitivities of ~0.1–0.2 mJy beam-1. All 24 LDQs show detectable radio structure in their nuclei. All 19 objects for which VLBI images could be made show one-sided nuclear jets, often several milliarcseconds in length and significantly curved, on the same side of the compact core as the one-sided large-scale jets seen on Very Large Array images. No counterjets were observed; jet-to-counterjet ratios that virtually all exceed ~10 suggest that these objects are all oriented within ~70° to the line of sight. For the 10 sources in which parsec-scale jet speeds could be estimated, the well-defined motions range from h-1c to ~4h-1c; some ambiguous cases might allow for motions as fast as ~8h-1c, even then they are not indicative of bulk Lorentz factors, γ, in excess of ~10h-1 (H0 = 100h km s-1 Mpc-1, q0 = 0.5). While the present distribution of jet speeds is consistent with random orientations, it is more easily accomodated by a restricted range of orientations. Evidence for slower jet speeds and larger apparent bends close to the core support the concept of a transition zone in the inner few parsecs of these jets. There are significant correlations among the prominences of the cores and jets, relative jet length, maximum jet deflection angles, and variability amplitude, as well as possible trends involving jet speed and strength of compact jet knots; furthermore, these objects tend to exhibit flat-spectrum cores and steep-spectrum jets. These results are all consistent with orientation-dependent relativistic beaming effects and unification of core- and lobe-dominated quasars. We have also defined a new postulated measure of orientation, based on both prominence of the radio nucleus and projected linear size, that correlates very well with properties predicted to have strong orientation dependence on beaming models. Finally, we confirm earlier studies demonstrating an anticorrelation between the prominence of the radio nucleus and the width of broad Mg II λ2798 optical emission lines; we also extend this result to C III] λ1909 and, more generally, to all broad lines by simple scaling and normalization methods. This relationship suggests a restricted range of orientations for LDQs, and that the broad-line clouds may have a flattened distribution associated with the accretion zone surrounding a central supermassive black hole.
Published: 2002

17. CJ-F: The Kinematics of 241 AGN

Author: T. J. Pearson, Silke Britzen, R. C. Vermeulen, P. N. Wilkinson, G. B. Taylor, Ian Browne, A. C. S. Readhead, and Robert M. Campbell
Subjects: Physics, Classical mechanics, 010504 meteorology & atmospheric sciences, 0103 physical sciences, Astrophysics, Kinematics, 010303 astronomy & astrophysics, 01 natural sciences, 0105 earth and related environmental sciences
Abstract: We present first results from the analysis of multi-epoch VLBI observations of 241 sources in the CJ-F sample (Caltech Jodrell-Flat-spectrum, Taylor et al. 1996). We have been obtaining 5 GHz VLBI (global and VLBA) snapshot observations of the CJ-F sources (complete with 293 sources) since 1990 in order to create a valid database for thorough statistical tests of pc-scale jet motion in AGN. All 241 CJ-F AGN have been observed at least three times with the VLBA, which enables us to investigate jet component motions and paths. In particular, we concentrate on the analysis of those properties supposed to be essential for gamma-ray production, i.e., superluminal motion and bending.
Published: 2001

18. H [CSC]i[/CSC] Absorption in the Steep-Spectrum Superluminal Quasar 3C 216

Author: Ylva Pihlström, John Conway, R. C. Vermeulen, and G. B. Taylor
Subjects: Physics, Superluminal motion, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Spectral line, Redshift, Radio telescope, Space and Planetary Science, Very-long-baseline interferometry, Hydrogen line, Astrophysics::Galaxy Astrophysics, Line (formation)
Abstract: The search for H I absorption in strong compact steep-spectrum sources is a natural way to probe the neutral gas contents in young radio sources. In turn, this may provide information about the evolution of powerful radio sources. The recently improved capabilities of the Westerbork Synthesis Radio Telescope have made it possible to detect a 0.31% (19 mJy) deep neutral atomic hydrogen absorption line associated with the steep-spectrum superluminal quasar 3C 216. The redshift (z = 0.67) of the source shifts the frequency of the 21 cm line down to the ultra-high-frequency (UHF) band (850 MHz). The exact location of the H I-absorbing gas remains to be determined by spectral line VLBI observations at 850 MHz. We cannot exclude that the gas might be extended on galactic scales, but we think it is more likely to be located in the central kiloparsec. Constraints from the lack of X-ray absorption probably rule out obscuration of the core region, and we argue that the most plausible site for the H I absorption is in the jet-cloud interaction observed in this source.
Published: 1999

19. VLBA multi-frequency monitoring of SS433

Author: R. T. Schilizzi, I. Fejes, Zsolt Paragi, Ralph Spencer, A. M. Stirling, and R. C. Vermeulen
Subjects: Physics, Jet (fluid), Epoch (reference date), Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Fractional polarization, Space and Planetary Science, Very-long-baseline interferometry, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract: We present results of VLBA observations of SS433 at two epochs at 5, 8.4, and 15 GHz. The AU-scale region of the source is resolved and shows the familiar quasi-symmetric core-jet structures. But at another epoch, the maps show bright knots ejected a few days before the observation, while the core-complex disappeared. The bright jet components are completely depolarised with fractional polarization less than 0.5%. We also present the first VLBI image of SS433 at 22 GHz.
Published: 1999

20. The Proper Motion of Sagittarius A*. I. First VLBA Results

Author: R. C. Vermeulen, Mark J. Reid, R. N. Treuhaft, and A. C. S. Readhead
Subjects: Physics, Solar mass, Proper motion, Astrophysics::High Energy Astrophysical Phenomena, Galactic Center, Astronomy and Astrophysics, Contact binary, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Galaxy, Luminosity, Black hole, symbols.namesake, Space and Planetary Science, Eddington luminosity, symbols, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract: We observed Sgr A* and two extragalactic radio sources nearby in angle with the VLBA over a period of two years and measured relative positions with an accuracy approaching 0.1 mas. The apparent proper motion of Sgr A* relative to J1745-283 is 5.90 +/- 0.4 mas/yr, almost entirely in the plane of the Galaxy. The effects of the orbit of the Sun around the Galactic Center can account for this motion, and any residual proper motion of Sgr A*, with respect to extragalactic sources, is less than about 20 km/s. Assuming that Sgr A* is at rest at the center of the Galaxy, we estimate that the circular rotation speed in the Galaxy at the position of the Sun is 219 +/- 20 km/s, scaled by Ro/8.0 kpc. Current observations are consistent with Sgr A* containing all of the nearly 2.6 x 10^6 solar masses, deduced from stellar proper motions, in the form of a massive black hole. While the low luminosity of Sgr A*, for example, might possibly have come from a contact binary containing of order 10 solar masses, the lack of substantial motion rules out a "stellar" origin for Sgr A*. The very slow speed of Sgr A* yields a lower limit to the mass of Sgr A* of about 1,000 solar masses. Even for this mass, Sgr A* appears to be radiating at less than 0.1 percent of its Eddington limit.
Published: 1999

21. Deep 8.4 GHz VLBI Images of Seven Faint Nuclei in Lobe‐dominated Quasars

Author: R. W. Porcas, T. A. Rector, Antonio Rius, A. C. S. Readhead, J. C. Snowdall, R. C. Vermeulen, D. H. Hough, G. C. Lenz, J. A. Zensus, and M. A. Davis
Subjects: Physics, Interferometry, Line-of-sight, Astrophysical jet, Space and Planetary Science, Radio galaxy, Very-long-baseline interferometry, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics, Position angle, Galaxy
Abstract: We present deep 8.4 GHz VLBI images of the faint nuclei in seven lobe-dominated quasars (LDQs): 3C 175, 3C 204, 3C 205, 3C 215, 3C 351, 0821)447, and 0839)616 . These images, made from data obtained in 1988 and 1991 with high-sensitivity VLBI arrays, have a typical rms noise level of D0.03 mJy per beam and resolution of D0.5 mas. The parsec-scale jet structures are generally greater in extent and complexity than those seen on many previous, less sensitive maps of other LDQ nuclei; the jet in 3C 204 bends through at least 10i, and the jet in 3C 205 extends out to D5 mas. Observations of 3C 204, 3C 205, and 0839)616 at two epochs reveal clear —ux density variability in 3C 204 and 3C 205, but none of these sources shows any evidence for outward motion of jet components; their mean appar- ent transverse velocity is ((0.47 ^ 0.43)h~1c, from which we determine a 3 p upper limit on their mean expansion speed of D0.8 h~1c km s~1 Mpc~1, The innermost jet knot in 3C 204 (H 0 \ 100 hq 0 \ 0.5). underwent a marginal position angle swing away from the mean jet axis. We also present the —rst 8.4 GHz A-array VLA images for all the objects except 3C 351. All the sources except 0821)447 display one-sided VLBI and VLA jets, which lie on the same side of the VLBI core and are generally well aligned (to within D5i). In addition, we analyze the statistics of projected linear size, relative nuclear strength, and misalignment angle for the 3CR and Jodrell Bank LDQ samples. We conclude that our results are generally consistent with a fairly simple relativistic jet model and with the uni—cation of core- dominated quasars, lobe-dominated quasars, and possibly even powerful radio galaxies; there is a mar- ginal suggestion that the quasars in our samples have a restricted range of angles to the line of sight (e.g., 0i to D45i). Subject headings: galaxies: jetsgalaxies: structurequasars: generalradio continuum: galaxies ¨ techniques: interferometric
Published: 1999

22. A Radio Millihalo in the Nucleus of NGC 1275

Author: G. B. Taylor, R. C. Vermeulen, and C. S. Silver
Subjects: Physics, Active galactic nucleus, Radio galaxy, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics, Relativistic particle, Hubble sequence, Peculiar galaxy, symbols.namesake, Astrophysical jet, Radio halo, Space and Planetary Science, symbols
Abstract: We present high dynamic range (20,000:1 at 1414 MHz) VLBA observations of NGC 1275 (3C 84) at 1414, 612, and 330 MHz. With these observations, we have discovered a previously undetected counterjet component located ~80 mas (20 h-1 pc) to the north of the compact core. This counterjet component, like those closer in to the nucleus, appears to be free-free absorbed. We have also discovered the first radio halo around an active galactic nucleus on small (
Published: 1998

23. Discovery of Twin Relativistic Jets in the Nearby E/S0 Galaxy NGC 3894

Author: J. M. Wrobel, G. B. Taylor, and R. C. Vermeulen
Subjects: Physics, Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Galaxy merger, Disc galaxy, Peculiar galaxy, Astrophysical jet, Space and Planetary Science, Interacting galaxy, Lenticular galaxy, Astrophysics::Galaxy Astrophysics, Dwarf galaxy
Abstract: VLBI techniques were used to monitor the milliarcsecond-scale continuum structure of the E/S0 galaxy NGC 3894. The resulting VLBI images span 15 yr and provide morphological and spectral evidence for twin, parsec-scale jets emerging from a synchrotron-self-absorbed core. Analysis of the twin-jet kinematics requires that the jets be both mildly relativistic (v ~ 0.3c) and oriented well away from the line of sight (θ ~ 50°). Slow jets could be deflected or disrupted, so evidence for such processes is examined. A large viewing angle could influence the galaxy's nuclear properties at other wavebands, and those properties are explored.
Published: 1998

24. Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei

Author: Maurice Cohen, R. C. Vermeulen, K. I. Kellermann, and J. A. Zensus
Subjects: Physics, 010504 meteorology & atmospheric sciences, biology, Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, Resolution (electron density), Astronomy and Astrophysics, Quasar, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, biology.organism_classification, 01 natural sciences, Spectral line, Luminosity, Wavelength, Space and Planetary Science, 0103 physical sciences, Egret, Absorption (electromagnetic radiation), 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences
Abstract: We have used the VLBA at 15 GHz to image the structure of 132 strong compact AGN and quasars with a resolution better than one milliarcsecond and a dynamic range typically exceeding 1000 to 1. These observations were made as part of a program to investigate the sub-parsec structure of quasars and AGN and to study the changes in their structure with time. Many of the sources included in our study, particularly those located south of +35 degrees, have not been previously imaged with milliarcsecond resolution. Each of the sources has been observed at multiple epochs. In this paper we show images of each of the 132 sources which we have observed. For each source we present data at the epoch which had the best quality data. The milliarcsecond jets generally appear one-sided but two-sided structure is often found in lower luminosity radio galaxies and in high luminosity quasars with gigahertz peaked spectra. Usually the structure is unresolved along the direction perpendicular to the jet, but a few sources have broad plumes. In some low luminosity radio galaxies, the structure appears more symmetric at 2 cm than at long wavelengths. The apparent long wavelength symmetry in these sources is probably due to absorption by intervening material. A few sources contain only a single component with any secondary feature at least a thousand times weaker. We find no obvious correlation of radio morphology and the detection of gamma-ray emission by EGRET.
Published: 1998

25. Pks 0116+082: An Optically Variable Compact Steep‐spectrum Source in A Narrow‐line Radio Galaxy

Author: Maurice Cohen, R. C. Vermeulen, P. M. Ogle, Hien D. Tran, and R. W. Goodrich
Subjects: Physics, Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Polarimetry, Synchrotron radiation, Astronomy and Astrophysics, Optical polarization, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Galaxy, law.invention, Telescope, Space and Planetary Science, law, OVV quasar, Astrophysics::Galaxy Astrophysics, BL Lac object
Abstract: Polarimetry of the narrow-line radio galaxy PKS 0116+082 at the W.M. Keck telescope shows that it has high and variable optical polarization, presumably due to synchrotron radiation. It is not a BL Lac object because it has strong narrow lines, and it is not an OVV quasar because it has no broad lines and the extended galaxy is prominent. VLA and VLBA images show that it is a compact steep-spectrum radio source with most of the emission coming from a region less than 100 milli-arcsec in size. Of the 25 compact steep-spectrum or gigahertz peaked-spectrum sources measured polarimetrically, four have high optical polarization. One of these has been observed only once but in the other three the polarization is variable. This gives an intriguing hint that variability may be a general property of these objects.
Published: 1997

26. Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes

Author: Olaf Wucknitz, J. Kohler, D. D. Mulcahy, Aris Karastergiou, M. Iacobelli, Wilfred Frieswijk, Michael W. Wise, Gianni Bernardi, Philip Best, Gerard H. Kuper, V. I. Kondratiev, M. Pandey-Pommier, Y. Tang, Tim Hassall, Sarod Yatawatta, P. Maat, R. J. van Weeren, Evan Keane, George Heald, Frank Breitling, A. Noutsos, S. Duscha, H. Munk, R. C. Vermeulen, W. N. Brouw, J. Eisloeffel, John McKean, Stefan J. Wijnholds, T. Grit, Heino Falcke, J. Sluman, Roberto Pizzo, C. Tasse, Jean-Mathias Griessmeier, Rob Fender, I. M. Avruch, G. de Bruyn, Carlos Sotomayor-Beltran, Sera Markoff, M. Brueggen, Ralph A. M. J. Wijers, B. Ciardi, E. Juette, S. ter Veen, A. W. Gunst, Chiara Ferrari, M. Kuniyoshi, J. W. Broderick, Giulia Macario, Matthias Hoeft, A. Horneffer, M. Pilia, Michel Tagger, Jason W. T. Hessels, F. de Gasperin, Annalisa Bonafede, Richard Fallows, A. Alexov, Luitje Koopmans, Martin Bell, M. A. Garrett, Rainer Beck, M. Serylak, Michael Kramer, P. Zarka, Huub Roettgering, J. van Leeuwen, James M. Anderson, R. J. Dettmar, Mark J. Bentum, Ben Stappers, A. G. Polatidis, Laura Birzan, Ashish Asgekar, Charlotte Sobey, Emanuela Orrú, Michael R. Bell, A. van Duin, H. Paas, W. Reich, Astronomisches Institut der Ruhr-Universität Bochum, Ruhr-Universität Bochum [Bochum], Max-Planck-Institut für Radioastronomie (MPIFR), University of Amsterdam [Amsterdam] (UvA), Netherlands Institute for Radio Astronomy (ASTRON), SRON Netherlands Institute for Space Research (SRON), Laboratoire de Chimie Physique Moléculaire (LCPM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, University of Edinburgh, Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), University of Southampton, Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Thüringer Landessternwarte Tautenburg (TLS), Radboud university [Nijmegen], Institute of Mathematical and Physical Sciences, Joseph Louis LAGRANGE (LAGRANGE), 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), 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), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), 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), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Oxford Astrophysics, University of Oxford [Oxford], Centre for Astrophysics and Supercomputing, Swinburne University of Technology [Melbourne], Karlsruhe Institute of Technology (KIT), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), Center for Information Technology CIT, Université de 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-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), 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), Astronomy, Kapteyn Astronomical Institute, High Energy Astrophys. & Astropart. Phys (API, FNWI), Harvard University-Smithsonian Institution, Universiteit Leiden, Radboud University [Nijmegen], 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), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), University of Oxford, 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), Sotomayor-Beltran, C., Sobey, C., Hessels, J.W.T., De Bruyn, G., Noutsos, A., Alexov, A., Anderson, J., Asgekar, A., Avruch, I.M., Beck, R., Bell, M.E., Bell, M.R., Bentum, M.J., Bernardi, G., Best, P., Birzan, L., Bonafede, A., Breitling, F., Broderick, J., Brouw, W.N., Brüggen, M., Ciardi, B., De Gasperin, F., Dettmar, R.-J., Van Duin, A., Duscha, S., Eislöffel, J., Falcke, H., Fallows, R.A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M.A., Grießmeier, J., Grit, T., Gunst, A.W., Hassall, T.E., Heald, G., Hoeft, M., Horneffer, A., Iacobelli, M., Juette, E., Karastergiou, A., Keane, E., Kohler, J., Kramer, M., Kondratiev, V.I., Koopmans, L.V.E., Kuniyoshi, M., Kuper, G., Van Leeuwen, J., Maat, P., MacArio, G., Markoff, S., McKean, J.P., Mulcahy, D.D., Munk, H., Orru, E., Paas, H., Pandey-Pommier, M., Pilia, M., Pizzo, R., Polatidis, A.G., Reich, W., Röttgering, H., Serylak, M., Sluman, J., Stappers, B.W., Tagger, M., Tang, Y., Tasse, C., Ter Veen, S., Vermeulen, R., Van Weeren, R.J., Wijers, R.A.M.J., Wijnholds, S.J., Wise, M.W., Wucknitz, O., Yatawatta, S., and Zarka, P.
Subjects: 010504 meteorology & atmospheric sciences, Astronomy, VLA, Polarimetry, FOS: Physical sciences, IR-89498, Astrophysics::Cosmology and Extragalactic Astrophysics, Rotation, 01 natural sciences, law.invention, Radio telescope, PULSAR ROTATION, symbols.namesake, MHZ, Pulsar, DISPERSION, law, 0103 physical sciences, Faraday effect, DEPOLARIZATION, Faraday cage, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, EWI-24501, polarization, Astrophysics::Instrumentation and Methods for Astrophysics, METIS-302716, Astronomy and Astrophysics, GALACTIC MAGNETIC-FIELD, LOFAR, Astronomy and Astrophysic, GALAXY, techniques: polarimetric, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics], ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, symbols, ARRAY, Ionosphere, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: International audience; Faraday rotation measurements using the current and next generation of low-frequency radio telescopes will provide a powerful probe of astronomical magnetic fields. However, achieving the full potential of these measurements requires accurate removal of the time-variable ionospheric Faraday rotation contribution. We present ionFR, a code that calculates the amount of ionospheric Faraday rotation for a specific epoch, geographic location, and line-of-sight. ionFR uses a number of publicly available, GPS-derived total electron content maps and the most recent release of the International Geomagnetic Reference Field. We describe applications of this code for the calibration of radio polarimetric observations, and demonstrate the high accuracy of its modeled ionospheric Faraday rotations using LOFAR pulsar observations. These show that we can accurately determine some of the highest-precision pulsar rotation measures ever achieved. Precision rotation measures can be used to monitor rotation measure variations - either intrinsic or due to the changing line-of-sight through the interstellar medium. This calibration is particularly important for nearby sources, where the ionosphere can contribute a significant fraction of the observed rotation measure. We also discuss planned improvements to ionFR, as well as the importance of ionospheric Faraday rotation calibration for the emerging generation of low-frequency radio telescopes, such as the SKA and its pathfinders.
Published: 2013

27. Structure and evolution of the compact radio source in NGC 1275

Author: Jonathan D. Romney, J. M. Benson, K. I. Kellermann, R. C. Vermeulen, R. C. Walker, and Vivek Dhawan
Subjects: Physics, Jet (fluid), Multidisciplinary, Accretion (meteorology), Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Parsec, Core (optical fiber), Interferometry, Feature (computer vision), New General Catalogue, Cutoff, Research Article
Abstract: Investigations of the fine-scale structure in the compact nucleus of the radio source 3C 84 in NGC 1275 (New General Catalogue number) are reported. Structural monitoring observations beginning as early as 1976, and continuing to the present, revealed subluminal motions in a jet-like relatively diffuse region extending away from a flat-spectrum core. A counterjet feature was discovered in 1993, and very recent nearly simultaneous studies have detected the same feature at five frequencies ranging from 5 to 43 GHz. The counterjet exhibits a strong low-frequency cutoff, giving this region of the source an inverted spectrum. The observations are consistent with a physical model in which the cutoff arises from free-free absorption in a volume that surrounds the core but obscures only the counterjet feature. If such a model is confirmed, very-long-baseline radio interferometry observations can then be used to probe the accretion region, outside the radio jet, on parsec scales.
Published: 1995

28. Superluminal sources

Author: R C Vermeulen
Subjects: Physics, education.field_of_study, Multidisciplinary, Superluminal motion, Deceleration parameter, Population, Quasar, Astrophysics, Galaxy, Luminosity, symbols.namesake, symbols, Source counts, education, Research Article, Hubble's law
Abstract: Predictions for the apparent velocity statistics under simple beaming models are presented and compared to the observations. The potential applications for tests of unification models and for cosmology (source counts, measurements of the Hubble constant H0 and the deceleration parameter q0) are discussed. First results from a large homogeneous survey are presented. The data do not show compelling evidence for the existence of intrinsically different populations of galaxies, BL Lacertae objects, or quasars. Apparent velocities betaapp in the range 1-5 h-1, where h = H0/100 km.s-1.Mpc-1 [1 megaparsec (Mpc) = 3.09 x 10(22) m], occur with roughly equal frequency; higher values, up to betaapp = 10 h-1, are rather more scarce than appeared to be the case from earlier work, which evidently concentrated on sources that are not representative of the general population. The betaapp distribution suggests that there might be a skewed distribution of Lorentz factors over the sample, with a peak at gammab approximately 2 h-1 and a tail up to at least gammab approximately 10 h-1. There appears to be a clearly rising upper envelope to the betaapp distribution when plotted as a function of observed 5-GHz luminosity; a combination of source counts and the apparent velocity statistics in a larger sample could provide much insight into the properties of radio jet sources.
Published: 1995

29. ERRATUM: 'MOJAVE: MONITORING OF JETS IN AGN WITH VLBA EXPERIMENTS. V. MULTI-EPOCH VLBA IMAGES' (2009, AJ, 137, 3718)

Author: Maurice Cohen, Tuomas Savolainen, Yuri Y. Kovalev, Matthew L. Lister, Eduardo Ros, R. C. Vermeulen, Hugh D. Aller, Daniel C. Homan, M. F. Aller, J. A. Zensus, K. I. Kellermann, and Matthias Kadler
Subjects: Physics, Space and Planetary Science, Epoch (reference date), Astronomy, Astronomy and Astrophysics
Published: 2016

30. Corrigendum: A large light-mass component of cosmic rays at 1017–1017.5 electronvolts from radio observations

Author: Wilfred Frieswijk, M. P. van Haarlem, Anna M. M. Scaife, Vishambhar Pandey, M. C. Toribio, A. Horneffer, Michael Kramer, Jochen Eislöffel, S. ter Veen, Harvey Butcher, A. W. Gunst, J. van Leeuwen, Maaijke Mevius, G. van Diepen, E. de Geus, Sarod Yatawatta, Adam Stewart, Adam Deller, V. I. Kondratiev, M. Pandey-Pommier, Laura Rossetto, D. Carbone, A. Nelles, A. G. Polatidis, Tim Hassall, D. D. Mulcahy, James M. Anderson, S. Duscha, Ralph A. M. J. Wijers, J. Sluman, Roberto Pizzo, Marcus Brüggen, Rebecca McFadden, Hubertus Intema, E. Juette, Stijn Buitink, Satyendra Thoudam, Rob Fender, M. Serylak, R. C. Vermeulen, F. de Gasperin, Y. Tang, O. Scholten, Christian Vocks, J. W. Broderick, M. A. Garrett, P. Maat, M. J. Norden, John D. Swinbank, Heino Falcke, John McKean, H. J. A. Röttgering, Aris Karastergiou, Mark J. Bentum, M. Iacobelli, Arthur Corstanje, Sera Markoff, Benjamin Stappers, M. Tagger, Michael W. Wise, Gianni Bernardi, Jörg R. Hörandel, G. M. Loose, Dominik J. Schwarz, Martin Bell, C. Tasse, Frank Breitling, John Conway, Annalisa Bonafede, H. Paas, M. Steinmetz, Gottfried Mann, R. J. Dettmar, Stefan J. Wijnholds, George Heald, Jason W. T. Hessels, T. Huege, Oleg Smirnov, W. N. Brouw, P. Zarka, J.-M. Grießmeier, B. Ciardi, D. Engels, O. Wucknitz, J. E. Enriquez, M. Kuniyoshi, Richard Fallows, G. Kuper, W. Reich, M. Pietka, Emanuela Orrú, Ashish Asgekar, C. Vogt, Philip Best, Pim Schellart, J. P. Rachen, H. Munk, R. J. van Weeren, D. McKay-Bukowski, Chiara Ferrari, T. N. G. Trinh, Matthias Hoeft, J. A. Zensus, I. M. Avruch, Department of Astrophysics [Nijmegen], Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud university [Nijmegen]-Radboud university [Nijmegen], Radboud university [Nijmegen], Karlsruher Institut für Technologie (KIT), Institute for Mathematics Applied to Geoscience, National Center for Atmospheric Research [Boulder] (NCAR), Netherlands Institute for Radio Astronomy (ASTRON), SRON Netherlands Institute for Space Research (SRON), CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), University of Edinburgh, Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), University of Southampton, Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], University of Amsterdam [Amsterdam] (UvA), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Medstar Research Institute, Astronomisches Institut der Ruhr-Universität Bochum, Ruhr-Universität Bochum [Bochum], Thüringer Landessternwarte Tautenburg (TLS), Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Institut de Génomique Fonctionnelle de Lyon (IGFL), École normale supérieure - Lyon (ENS Lyon)-Institut National de la Recherche Agronomique (INRA)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS), Département de Géologie, Université de Montréal [Montréal], Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Rhodes University, Max-Planck-Institut für Radioastronomie (MPIFR), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Oulu, Center for Information Technology CIT, Université de Groningen, Centre de Recherche Astrophysique de Lyon (CRAL), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon), Department of Physics and Astronomy [Ghent], Ghent University [Belgium] (UGENT), Oxford Astrophysics, University of Oxford [Oxford], School of Physics and Astronomy [Southampton], 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), 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)-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)-Centre National d’Études Spatiales [Paris] (CNES), 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 Libre de Bruxelles [Bruxelles] (ULB), 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), Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, 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), Radboud University [Nijmegen]-Radboud University [Nijmegen], Radboud University [Nijmegen], École normale supérieure de Lyon (ENS de Lyon)-Institut National de la Recherche Agronomique (INRA)-Université Claude Bernard Lyon 1 (UCBL), Université de Montréal (UdeM), Universiteit Leiden, Rhodes University, Grahamstown, 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), Universiteit Gent = Ghent University (UGENT), University of Oxford, 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), 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), Université libre de Bruxelles (ULB), 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), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut National de la Recherche Agronomique (INRA)-École normale supérieure - Lyon (ENS Lyon), 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), Universiteit Gent = Ghent University [Belgium] (UGENT), 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, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES)
Subjects: Pierre Auger Observatory, Astroparticle physics, Physics, [PHYS]Physics [physics], Multidisciplinary, 010504 meteorology & atmospheric sciences, High-energy astronomy, Astronomy, Electronvolt, Cosmic ray, LOFAR, Astrophysics, 01 natural sciences, Auger, International Cosmic Ray Conference, 0103 physical sciences, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract: In this Letter, we omitted to cite preliminary results from the low-energy extension of the Pierre Auger Observatory, as presented at the International Cosmic Ray Conference 2015 (ref. 1). Figure 1 of this Corrigendum shows measurements of the average value of Xmax for the Low Frequency Array (LOFAR), and earlier experiments using different techniques, now including the data from the Pierre Auger Observatory1 , specifically the contribution of A. Porcelli. Our values are in agreement with those of ref. 1 within systematic uncertainties.
Published: 2016

31. Wide-band simultaneous observations of pulsars: disentangling dispersion measure and profile variations

Author: P. Maat, Benjamin Stappers, Heino Falcke, Charlotte Sobey, Emanuela Orrú, Jason W. T. Hessels, E. Rol, L. Bähren, H. Meulman, Joris P. W. Verbiest, C. Tasse, A. Alexov, Matthias Hoeft, M. A. Garrett, Sarod Yatawatta, James Miller-Jones, Evan Keane, Michael Kramer, S. ter Veen, J. Masters, A. W. Gunst, Casey J. Law, Jochen Eislöffel, B. Scheers, Maaijke Mevius, T. E. Hassall, J. W. Broderick, R. C. Vermeulen, B. Ciardi, Martin Bell, John McKean, Luitje Koopmans, J. E. Noordam, Gerard H. Kuper, Annalisa Bonafede, Harvey Butcher, Sera Markoff, M. P. van Haarlem, E. J. Daw, Rudy Wijnands, M. Kuniyoshi, V. I. Kondratiev, M. Pandey-Pommier, A. Noutsos, K. Zagkouris, Michael R. Bell, H. Paas, J. Sluman, Michiel A. Brentjens, Ashish Asgekar, Roberto Pizzo, Marcus Brüggen, C. G. M. Sterks, W. Reich, R. A. Osten, Albert-Jan Boonstra, Michel Tagger, Stephane Corbel, A. G. Polatidis, P.G. Jonker, M. Gerbers, Stefan J. Wijnholds, J. van Leeuwen, H. Spreeuw, A. de Jong, Matthias Steinmetz, R. J. van Weeren, P. Zarka, K. Lazaridis, George Heald, Mark J. Bentum, G. M. Loose, W. N. Brouw, Patrick Weltevrede, V. S. Dhillon, Aris Karastergiou, Michael W. Wise, Gianni Bernardi, M. Serylak, Rob Fender, Ralph A. M. J. Wijers, H. J. A. Röttgering, H. A. Holties, Y. Tang, Anna M. M. Scaife, Olaf Wucknitz, H. Munk, John D. Swinbank, Jean-Mathias Griessmeier, Vishambhar Pandey, Philip Best, Pim Schellart, T. Coenen, Kenneth C. Anderson, Kapteyn Astronomical Institute, Astronomy, Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Netherlands Institute for Radio Astronomy (ASTRON), Max-Planck-Institut für Radioastronomie (MPIFR), Oxford Astrophysics, University of Oxford [Oxford], 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), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), 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), University of Southampton, Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), 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 Sheffield [Sheffield], Thüringer Landessternwarte Tautenburg (TLS), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud university [Nijmegen], Space Telescope Science Institute (STSci), School of Physics and Astronomy [Southampton], 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), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, University of Edinburgh, Jacobs University [Bremen], Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Leiden Observatory [Leiden], Universiteit Leiden [Leiden], National Radio Astronomy Observatory (NRAO), Applied Stochastics (IMAPP), 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-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), Center for Information Technology CIT, Université de Groningen, Netherlands Foundation for Scientific Research. Joeri van Leeuwen and ThijsCoenen are supported by the Netherlands Research School for Astronomy (GrantNOVA3-NW3-2.3.1), European Project: 224838,EC:FP7:PEOPLE,FP7-PEOPLE-2007-4-3-IRG,PULSARS WITH LOFAR(2008), European Project: 236394,EC:FP7:PEOPLE,FP7-PEOPLE-IEF-2008,PULSAR SURVEY(2010), Hassall, T.E., Stappers, B.W., Hessels, J.W.T., Kramer, M., Alexov, A., Anderson, K., Coenen, T., Karastergiou, A., Keane, E.F., Kondratiev, V.I., Lazaridis, K., Van Leeuwen, J., Noutsos, A., Serylak, M., Sobey, C., Verbiest, J.P.W., Weltevrede, P., Zagkouris, K., Fender, R., Wijers, R.A.M.J., Bähren, L., Bell, M.E., Broderick, J.W., Corbel, S., Daw, E.J., Dhillon, V.S., Eislöffel, J., Falcke, H., Grießmeier, J.-M., Jonker, P., Law, C., Markoff, S., Miller-Jones, J.C.A., Osten, R., Rol, E., Scaife, A.M.M., Scheers, B., Schellart, P., Spreeuw, H., Swinbank, J., Ter Veen, S., Wise, M.W., Wijnands, R., Wucknitz, O., Zarka, P., Asgekar, A., Bell, M.R., Bentum, M.J., Bernardi, G., Best, P., Bonafede, A., Boonstra, A.J., Brentjens, M., Brouw, W.N., Brüggen, M., Butcher, H.R., Ciardi, B., Garrett, M.A., Gerbers, M., Gunst, A.W., Van Haarlem, M.P., Heald, G., Hoeft, M., Holties, H., De Jong, A., Koopmans, L.V.E., Kuniyoshi, M., Kuper, G., Loose, G.M., Maat, P., Masters, J., McKean, J.P., Meulman, H., Mevius, M., Munk, H., Noordam, J.E., Orrú, E., Paas, H., Pandey-Pommier, M., Pandey, V.N., Pizzo, R., Polatidis, A., Reich, W., Röttgering, H., Sluman, J., Steinmetz, M., Sterks, C.G.M., Tagger, M., Tang, Y., Tasse, C., Vermeulen, R., Van Weeren, R.J., Wijnholds, S.J., Yatawatta, S., University of Oxford, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), 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), Radboud University [Nijmegen], Harvard University-Smithsonian Institution, Universiteit Leiden, 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), High Energy Astrophys. & Astropart. Phys (API, FNWI), Université d'Orléans (UO)-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)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), 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), 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), Rhodes University, SKA South Africa, and Ska South Africa
Subjects: 010504 meteorology & atmospheric sciences, Astronomy, Magnetosphere, Astrophysics, magnetic fields, 01 natural sciences, law.invention, law, Dispersion (optics), 010303 astronomy & astrophysics, Telescope, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, [PHYS]Physics [physics], Astrophysics::Instrumentation and Methods for Astrophysics, SPECTRAL BEHAVIOR, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Astrophysics - High Energy Astrophysical Phenomena, ARRIVAL-TIME DELAY, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, SUPERDISPERSION DELAY, EMPIRICAL-THEORY, Pulsar, pulsars: general, 0103 physical sciences, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, ISM: general, METIS-287956, Gravitational wave, Astronomy and Astrophysics, telescopes, LOFAR, Astronomy and Astrophysic, EWI-22107, Pulse (physics), PULSES, Interstellar medium, PSR 0809&74, FREQUENCY-DEPENDENCE, Magnetic field, Space and Planetary Science, [SDU]Sciences of the Universe [physics], RADIO-EMISSION, IR-80985, REFRACTION, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], INTERSTELLAR SCATTERING
Abstract: Dispersion in the interstellar medium is a well known phenomenon that follows a simple relationship, which has been used to predict the time delay of dispersed radio pulses since the late 1960s. We performed wide-band simultaneous observations of four pulsars with LOFAR (at 40-190 MHz), the 76-m Lovell Telescope (at 1400 MHz) and the Effelsberg 100-m Telescope (at 8000 MHz) to test the accuracy of the dispersion law over a broad frequency range. In this paper we present the results of these observations which show that the dispersion law is accurate to better than 1 part in 100000 across our observing band. We use this fact to constrain some of the properties of the ISM along the line-of-sight and use the lack of any aberration or retardation effects to determine upper limits on emission heights in the pulsar magnetosphere. We also discuss the effect of pulse profile evolution on our observations, and the implications that it could have for precision pulsar timing projects such as the detection of gravitational waves with pulsar timing arrays., 20 Pages, 14 Figures, Accepted for publication in Astronomy & Astrophysics
Published: 2012

32. VLBA Observations of HI in the Archetype Compact Symmetric Object B2352+495

Author: Ylva Pihlström, G. B. Taylor, Cristina Rodríguez, R. C. Vermeulen, S. E. Tremblay, and E. D. Araya
Subjects: Physics, Supermassive black hole, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Redshift, Spectral line, Galaxy, Space and Planetary Science, Absorption (electromagnetic radiation), Very Long Baseline Array, Astrophysics::Galaxy Astrophysics, Line (formation), Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: B2352+495 is a prototypical example of a Compact Symmetric Object (CSO). It has a double radio lobe symmetrically located with respect to a central flat spectrum radio core (the location of the AGN) and has a physical extent of less than 200 pc. In this work we report VLBA observation of 21 cm HI absorption toward B2352+495 to investigate the properties of this remarkable radio source, in particular, to explore whether the radio emission can be confined by circumnuclear material (frustration scenario) or whether the source is likely to be young. We confirmed the two HI absorption features previously detected toward B2352+495 - a broad line nearly centered at the systemic velocity of the galaxy and a narrow redshifted component. The atomic gas from the broad absorption component is likely associated with circumnuclear material, consistent with the current paradigm of clumpy HI distribution in toroidal structures around supermassive black holes., 25 pages, 4 figures. Accepted for publication in the Astronomical Journal
Published: 2009

33. MOJAVE: monitoring of jets in active galactic nuclei with VLBA experiments. V. Multi-epoch VLBA images

Author: Matthias Kadler, K. I. Kellermann, J. A. Zensus, Eduardo Ros, Maurice Cohen, Matthew L. Lister, D. C. Homan, Hugh D. Aller, Margo F. Aller, Yuri Y. Kovalev, Tuomas Savolainen, and R. C. Vermeulen
Subjects: Physics, Jet (fluid), Active galactic nucleus, 010308 nuclear & particles physics, Epoch (astronomy), media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Declination, CTA-102, Relativistic beaming, 13. Climate action, Space and Planetary Science, Sky, 0103 physical sciences, Blazar, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, media_common
Abstract: We present images from a long-term program (MOJAVE: Monitoring of Jets in active galactic nuclei (AGNs) with VLBA Experiments) to survey the structure and evolution of parsec-scale jet phenomena associated with bright radio-loud active galaxies in the northern sky. The observations consist of 2424 15 GHz Very Long Baseline Array (VLBA) images of a complete flux-density-limited sample of 135 AGNs above declination –20°, spanning the period 1994 August to 2007 September. These data were acquired as part of the MOJAVE and 2 cm Survey programs, and from the VLBA archive. The sample-selection criteria are based on multi-epoch parsec-scale (VLBA) flux density, and heavily favor highly variable and compact blazars. The sample includes nearly all the most prominent blazars in the northern sky, and is well suited for statistical analysis and comparison with studies at other wavelengths. Our multi-epoch and stacked-epoch images show 94% of the sample to have apparent one-sided jet morphologies, most likely due to the effects of relativistic beaming. Of the remaining sources, five have two-sided parsec-scale jets, and three are effectively unresolved by the VLBA at 15 GHz, with essentially all of the flux density contained within a few tenths of a milliarcsecond.
Published: 2009

34. Exploring the limits of Phase Referenced VLBI Imaging; a progress report

Author: J. E. Conway and R. C. Vermeulen
Subjects: Physics, Coherence time, Atmospheric models, Very-long-baseline interferometry, Phase (waves), Remote sensing
Abstract: The practical limits of phase referenced VLBI imaging are not well known. If it would be feasible to use target-reference separations of a few degrees, most of the sky would be accessible to the technique. Preliminary results at 6 cm using baselines of up to 1000 km are encouraging.
Published: 1991

35. Intrinsic Brightness Temperatures of AGN Jets

Author: Yuri Y. Kovalev, R. C. Vermeulen, J. A. Zensus, Matthew L. Lister, Daniel C. Homan, Matthias Kadler, Eduardo Ros, Marshall H. Cohen, and K. I. Kellermann
Subjects: Physics, Brightness, Jet (fluid), Superluminal motion, Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, 010305 fluids & plasmas, Magnetic field, Intrinsic brightness, Space and Planetary Science, Brightness temperature, 0103 physical sciences, galaxies : active, galaxies : jets, galaxies : kinematics and dynamics, radiation mechanisms : nonthermal, radio continuum : galaxies, active galactic nuclei, radio-sources, magnetic-field, quasars, variability, motion, iv, 010303 astronomy & astrophysics, Equipartition theorem, Caltech Library Services, Astrophysics::Galaxy Astrophysics
Abstract: We present a new method for studying the intrinsic brightness temperatures of the parsec-scale jet cores of Active Galactic Nuclei (AGN). Our method uses observed superluminal motions and observed brightness temperatures for a large sample of AGN to constrain the characteristic intrinsic brightness temperature of the sample as a whole. To study changes in intrinsic brightness temperature, we assume that the Doppler factors of individual jets are constant in time as justified by their relatively small changes in observed flux density. We find that in their median-low brightness temperature state, the sources in our sample have a narrow range of intrinsic brightness temperatures centered on a characteristic temperature, T_int = 3 x 10^10 K, which is close to the value expected for equipartition, when the energy in the radiating particles equals the energy stored in the magnetic fields. However, in their maximum brightness state, we find that sources in our sample have a characteristic intrinsic brightness temperature greater than 2 x 10^11 K, which is well in excess of the equipartition temperature. In this state, we estimate the energy in radiating particles exceeds the energy in the magnetic field by a factor of ~ 10^5. We suggest that the excess of particle energy when sources are in their maximum brightness state is due to injection or acceleration of particles at the base of the jet. Our results suggest that the common method of estimating jet Doppler factors by using a single measurement of observed brightness temperature and/or the assumption of equipartition may lead to large scatter or systematic errors in the derived values., Comment: 4 pages, 2 figures, Accepted to Appear in ApJ Letters
Published: 2006
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36. Jet Collimation in Action: Re-alignment on Kiloparsec Scales in 3C279

Author: J. A. Zensus, D. C. Homan, K. I. Kellermann, Matthew L. Lister, Matthias Kadler, Eduardo Ros, R. C. Vermeulen, and Maurice Cohen
Subjects: Physics, Jet (fluid), Astrophysics::High Energy Astrophysical Phenomena, media_common.quotation_subject, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Collimated light, Magnetic field, symbols.namesake, Lorentz factor, Space and Planetary Science, Sky, symbols, Trajectory, Doppler effect, Astrophysics::Galaxy Astrophysics, media_common
Abstract: We report a change in the trajectory of a well studied jet component of the quasar 3C279. The component changes in apparent projected speed and direction, and we find it to be moving with a Lorentz factor gamma >~ 15 at an initial angle of ~ 1 kiloparsec (deprojected) along the jet. While the change in trajectory on the sky appears to be 26 degrees the intrinsic change is ~ 28 and after the change to be D >~ 23. Comparison to independent constraints on the Doppler factor suggest that the energy in the radiating particles cannot greatly exceed the energy in the magnetic field unless the volume filling factor is very much less than one., Comment: 4 pages, 4 figures, Accepted by ApJ Letters. Replaced version adds a comment to the discussion
Published: 2003

37. The shroud around the twin radio jets in NGC 1052

Author: Eduardo Ros, J. A. Zensus, H. J. van Langevelde, K. I. Kellermann, Marshall H. Cohen, and R. C. Vermeulen
Subjects: Physics, High velocity, media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Synchrotron, Spectral line, law.invention, Space and Planetary Science, law, Sky, 0103 physical sciences, Very-long-baseline interferometry, Shroud, 010306 general physics, Spectroscopy, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, media_common
Abstract: (Abridged) We discuss multiple VLBI continuum and spectral line observations and WSRT spectroscopy of NGC 1052. Sub-parsec scale features move outward at approximately 0.26c in bi-symmetric jets, most likely oriented near the plane of the sky. Absorption and emission signatures reveal ionised, atomic, and molecular components of the surrounding medium. Seven-frequency (1.4 to 43 GHz) VLBA observations show free-free absorption in the inner parsec, probably together with synchrotron self-absorption. There is apparently a geometrically thick but patchy structure oriented roughly orthogonal to the jets. The western jet is receding: it is covered more deeply and extensively. HI spectral line VLBI reveals atomic gas in front of both jets. There appear to be three velocity systems. The deepest, at "high velocities" (receding by 125 to 200 km/s), seems restricted to a shell 1 to 2 pc away from the core, within which this gas might be largely ionised. WSRT spectroscopy has revealed 1667 and 1665 MHz OH absorption with their line ratio varying roughly from 1:1 to 2:1 between -35 and 200 km/s. In the high velocity system the OH profiles are similar to HI, suggesting co-location of that atomic and molecular gas, and leaving unclear the connection to the H2O masing gas seen elsewhere. We have also detected both 18cm OH satellite lines in the high velocity system. They have conjugate profiles: 1612 MHz is in absorption, and 1720 MHz in emission., Comment: 16 pages, 14 figures, LaTeX, includes aa.cls, accepted for publication in Astronomy and Astrophysics
Published: 2003

38. 4C +12.50: A Superluminal Precessing Jet in the Recent Merger System IRAS 13451+1232

Author: Maurice Cohen, R. C. Vermeulen, Matthew L. Lister, Eduardo Ros, K. I. Kellermann, and J. A. Zensus
Subjects: Physics, Jet (fluid), Superluminal motion, Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Astronomy, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Galaxy, Black hole, Space and Planetary Science, Precession, Very Long Baseline Array, Astrophysics::Galaxy Astrophysics
Abstract: We present the results of a multi-epoch VLBA study of the powerful radio source 4C +12.50 (PKS 1345+125) at a wavelength of 2 cm. This compact radio source is associated with a hidden quasar whose host galaxy shows signs of a recent merger. It has been classified as a compact symmetric source (CSO) due to its small overall size (~220 pc) and twin-jet morphology, although it also has faint extended emission that may be a relic of previous activity. We report the detection of exceedingly high linear fractional polarization in isolated features of the southern jet (up to 60%), which is highly unusual for a CSO. Given the large amount of gas present in the host galaxy, we would expect significant Faraday depolarization across the whole source, unless the depolarizing gas is fairly clumpy. The southern jet also contains two features that are moving outward from the core at apparent speeds of v/c = 1.0 +/- 0.3 and 1.2 +/- 0.3. These represent the first positive detections of superluminal motion in a CSO, and taken together with the jet to counter-jet flux ratio, suggest an intrinsic flow speed of v/c = 0.84 +/- 0.12. The apparent ridgeline of the jet and counter-jet are consistent with a conical helix of wavelength 280 pc that is the result of Kelvin-Helmholtz instabilities driven by a slow precession of the jet nozzle. A fit to the data implies that the nozzle is precessing around a cone with half-angle 23 degrees, whose axis lies at an angle of 82 degrees to the line of sight. We suggest that the "S"-shaped jet morphologies commonly seen in recent AGN outflows such as 4C +12.50 may simply reflect the fact that their black hole spin axes are still precessing, and have not had sufficient time to align with their accretion disks., Comment: 15 pages including 6 figures. Uses emulateapj.sty. Accepted for publication in the Astrophysical Journal
Published: 2002
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39. The properties of the gamma-ray blazars in the CJ-F VLBI sample

Author: Ian Browne, T. J. Pearson, Silke Britzen, P. N. Wilkinson, G. B. Taylor, A. C. S. Readhead, R. C. Vermeulen, Robert M. Campbell, Aharonian, Felix A., and Voelk, Heinrich J.
Subjects: Physics, Superluminal motion, Active galactic nucleus, biology, Very-long-baseline interferometry, Gamma ray, Egret, Astronomy, Astrophysics, biology.organism_classification, Galactic nuclei, Blazar, Caltech Library Services
Abstract: We present first results from the analysis of multi-epoch VLBI observations of the EGRET detected sources [9] in the CJ-F sample (Caltech Jodrell-Flat-spectrum, [10]). These objects form a subsample of 14 sources within the 293 AGN of the full CJ-F sample. 5 GHz VLBI snapshot observations of the CJ-F sources are continuously being performed in order to create a valid database for thorough statistical tests of pc-scale jet motion in AGN. All gamma-bright CJ-F AGN have been observed at least twice with the VLBA, which enables us to investigate jet component motions and paths. In particular, we concentrate on the analysis of those properties supposed to be essential for gamma-ray production, i.e., superluminal motion and bending. A paper discussing the possible relation between morphological changes and gamma-ray flaring/production is in preparation.
Published: 2001

40. Limits on the cosmological abundance of supermassive compact objects from a search for multiple imaging in compact radio sources

Author: D. R. Henstock, G. B. Taylor, W. Xu, T. J. Pearson, Pedro Augusto, Iwa Browne, R. C. Vermeulen, A. C. S. Readhead, A. G. Polatidis, and P. N. Wilkinson
Subjects: Physics, education.field_of_study, Supermassive black hole, Astrophysics::High Energy Astrophysical Phenomena, Dark matter, Population, Astrophysics (astro-ph), General Physics and Astronomy, Astronomy, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, General Relativity and Quantum Cosmology, Gravitational lens, Closure (mathematics), Very-long-baseline interferometry, Content (measure theory), Intergalactic travel, education
Abstract: Using Very Long Baseline Interferometry we have searched a sample of 300 compact radio sources for examples of multiple imaging produced by gravitational lensing; no multiple images were found with separations in the angular range 1.5--50 milliarcsec. This null result allows us to place a limit on the cosmological abundance of intergalactic supermassive compact objects in the mass range $\sim 10^{6}$ to $\sim 10^{8}$M$_{\odot}$; such objects cannot make up more than $\sim 1%$ of the closure density (95% confidence). A uniformly distributed population of supermassive black holes forming soon after the Big Bang do not, therefore, contribute significantly to the dark matter content of the Universe., Comment: 2 figures
Published: 2001
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41. Associated HI in Absorbers at High Redshift

Author: R. C. Vermeulen
Subjects: Physics, 010504 meteorology & atmospheric sciences, Astrophysics (astro-ph), Astronomy, FOS: Physical sciences, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Redshift, Ultra high frequency, 0103 physical sciences, Very-long-baseline interferometry, Hydrogen line, Absorption (electromagnetic radiation), 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Incidence (geometry), Line (formation)
Abstract: WSRT observations have provided a first inventory of the incidence of HI 21 cm line absorption associated with AGN at redshifts up to z=1.0. There is a large range in line depths, from tau=0.44 to tau less than 0.001, and a substantial variety of line profiles, from Gaussians of less than ten km/s to more typically a few hundred km/s, as well as irregular and multi-peaked absorption, sometimes spanning many hundreds of km/s. The chance to detect appreciable HI absorption is greatest in the most compact radio sources, GPSs and CSOs, where it can occur in circumnuclear ``disks'' or ``tori'', as well as in gas enveloping jets and hot spots; inferred densities range at least between 10 per cubic cm and 10000 per cubic cm. But HI absorption occurs also in some CSSs, perhaps associated with jet-cloud interaction regions, and in quasars with a large optical reddening. VLBI observations at the unusual UHF frequencies of redshifted HI 21 cm can give unique ``sight''lines into the physics and evolution of young radio sources and their inner galactic medium., 4 pages, 2 postscript figures, LaTeX, uses paspiau199.sty. to appear in "The Universe at Low Radio Frequencies", IAU Symposium 199, ASP Conference Series, V.K. Kapahi & A.P. Rao (eds.)
Published: 2000

42. Redshifts and Neutral Hydrogen Observations of Compact Symmetric Objects in the COINS Sample

Author: R. C. Vermeulen, Alison B. Peck, Anthony C. S. Readhead, G. B. Taylor, and Christopher D. Fassnacht
Subjects: Physics, Active galactic nucleus, Radio galaxy, media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Redshift, Accretion (astrophysics), Relativistic beaming, Space and Planetary Science, Sky, Very-long-baseline interferometry, Absorption (electromagnetic radiation), Astrophysics::Galaxy Astrophysics, media_common
Abstract: Compact Symmetric Objects (CSOs) are young radio galaxies whose jet axes lie close to the plane of the sky, and whose appearance is therefore not dominated by relativistic beaming effects. The small linear sizes of CSOs make them valuable for studies of both the evolution of radio galaxies and testing unified schemes for active galactic nuclei (AGN). A parsec-scale region of gas surrounding the central engine is predicted by both accretion and obscuration scenarios. Working surfaces, or ``hot spots,'' and the radio jets of CSOs are close enough to the central engines that this circumnuclear gas can be seen in absorption. The CSOs Observed in the Northern Sky (COINS) sample is comprised of 52 CSO candidates identified in three VLBI surveys. Of these, 27 have now been confirmed as CSOs. Optical redshifts are available in the literature for 28 of the CSO candidates, and HI absorption has been detected toward four. We present new optical spectroscopic redshifts for three of the candidates and summarize the current status of optical identifications. We further report on the discovery of HI in absorption towards the CSO J1816+3457 and summarize the results of neutral hydrogen absorption studies of the sources in this sample., 12 pages, Accepted for publication in ApJ
Published: 1999

43. VLBA Absorption Imaging of Ionized Gas Associated with the Accretion Disk in NGC 1275

Author: Kenneth I. Kellermann, R. C. Walker, Jonathan D. Romney, R. C. Vermeulen, and Vivek Dhawan
Subjects: Physics, Accretion disc, Space and Planetary Science, Central object, Magnitude (astronomy), Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Plasma, Astrophysics, Absorption (electromagnetic radiation), Spectral line
Abstract: Nearly simultaneous VLBA observations of 3C 84, the radio source associated with NGC 1275, have been made at multiple frequencies to study the free-free absorption of the northern, or "counterjet", feature found by Walker, Romney, and Benson (1994, Ap.J. 430, L45) and by Vermeulen, Readhead, and Backer (1994, Ap.J. 430, L41). Our observations confirm that the spectra are consistent with free-free absorption and eliminate the possibility that the earlier result was an effect of variability. The northern feature is well resolved spatially, so images have been made showing the distribution of the absorption over a region of about 1.5 pc on a side, beginning about 1.5 pc from the presumed location of the central object. That distribution is dominated by a strong decrease with radial distance. The magnitude of the absoption near 2.5 pc projected distance from the central object is consistent with a 10^4 K gas with an emission measure of about 5 X 10^8 pc cm^-6. The geometry is consistent with absorption by ionized gas associated with an accretion disk. The data provide firm constraints for models of the outer regions of accretion disks and, perhaps, associated winds., Comment: 24 pages, 9 figures. Accepted 1999 Sept. 9 for publication in the Astrophysical Journal
Published: 1999
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44. The Angular Size-Redshift Test for Compact Radio Sources in the Caltech-Jodrell Bank Surveys

Author: A. G. Polatidis, P. N. Wilkinson, S. Myles, G. B. Taylor, W. Xu, D. Alcock, A. C. S. Readhead, R. C. Vermeulen, T. J. Pearson, Ian Browne, and D. R. Henstock
Subjects: Physics, COSMIC cancer database, Epoch (astronomy), Angular distance, Angular diameter, Astrophysics::High Energy Astrophysical Phenomena, Electronic engineering, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Cosmology, Redshift
Abstract: In 1958 Hoyle first suggested that the angular separation of the components of large double radio sources might be used as a standard rod in the classical angular diameter vs. redshift (θ-z) test (Hoyle 1959). Thirty years and thousands of radio observations later this hope was finally dashed. Gradually it had become clear that the evolution of the intrinsic sizes of double radio sources with cosmic epoch completely masked the more subtle effects of universal geometry (e.g. Nilsson et al. 1993). It was therefore with some surprise that the community greeted the analyses of the angular sizes of the milliarcsecond jets in bright radio nuclei by Kellermann (1993) and Gurvits (1994). Rather than the monotonic fall-off of median angular size with redshift exhibited by double radio sources, the compact radio sources seemed to show the expected signature of standard relativistic cosmology i.e. an initial fall-off of θ with z followed by an approximately constant θ beyond z ∼ 0.5. Perhaps, as suggested by Kellermann (1993), the power and short lifetimes of these structures make them less susceptible to the environmental effects which bedevilled the test with double sources. Kellermann concluded his paper thus
Published: 1998

45. The Caltech-Jodrell Bank VLBI Surveys

Author: D. D. Thakkar, P. N. Wilkinson, A. C. S. Readhead, T. J. Pearson, R. C. Vermeulen, W. Xu, G. B. Taylor, A. G. Polatidis, D. R. Henstock, and Iwa Browne
Subjects: Physics, Superluminal motion, 010504 meteorology & atmospheric sciences, Astrophysics (astro-ph), Astronomy, FOS: Physical sciences, Astrophysics, 01 natural sciences, 7. Clean energy, Declination, Cosmology, Redshift, 13. Climate action, 0103 physical sciences, Very-long-baseline interferometry, 010303 astronomy & astrophysics, MERLIN, 0105 earth and related environmental sciences
Abstract: The Caltech-Jodrell Bank VLBI surveys of bright extragalactic radio sources north of declination 35 deg were carried out between 1990 and 1995 using the Mark-II system, achieving images with a resolution of about 1 mas at 5 GHz. The CJ1 survey (together with the older `PR' survey) includes 200 objects with 5 GHz flux density greater than 0.7 Jy; the CJ2 survey includes 193 flat-spectrum sources with 5 GHz flux density greater than 0.35 Jy; and we have defined a complete flux-density limited sample, CJF, of 293 flat-spectrum sources stronger than 0.35 Jy. We summarize the definition of the samples and the VLBI, VLA, MERLIN, and optical observations, and present some highlights of the astrophysical results. These include: (1) superluminal motion and cosmology; (2) morphology and evolution of the `compact symmetric objects' (CSOs); (3) two-sided motion in some CSOs; (4) the angular-size - redshift diagram; (5) misalignment of parsec-scale and kiloparsec-scale jets., Comment: 8 pages; 1 figure; to be published in Proceedings of IAU Colloquium 164, Radio Emission from Galactic and Extragalactic Compact Sources
Published: 1997
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46. Bi-Directional Relativistic Jets of the Radio Galaxy 1946+708: Constraints on the Hubble Constant

Author: G. B. Taylor and R. C. Vermeulen
Subjects: Length scale, Physics, Jet (fluid), 010504 meteorology & atmospheric sciences, Radio galaxy, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Kinematics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Symmetry (physics), Core (optical fiber), symbols.namesake, Astrophysical jet, Space and Planetary Science, 0103 physical sciences, symbols, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Hubble's law
Abstract: We present measurements of bi-directional motions in the jets of the radio galaxy 1946+708 at z=0.101. This is a Compact Symmetric Object with striking S-symmetry. Sensitive 15 GHz observations reveal a compact component at the center of symmetry with a strongly inverted spectrum, that we identify as the core. From five 4.9 GHz observations spread over 4 years we have determined the velocities of four compact jet components. If simple kinematic models can be applied then the inclination of the source and the bulk jet velocity can be directly determined for any assumed value of the Hubble constant. Conversely, the measurements already place constraints on the Hubble constant, and we show how further observations of 1946+708 can yield an increasingly accurate determination of H_0., Comment: in press at ApJ Letters, 12 page LaTex document includes 5 postscript figures
Published: 1997
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47. The Parsec-Scale Structure of NGC 1275 at 1.3 GHz

Author: G. B. Taylor and R. C. Vermeulen
Subjects: Physics, Core (optical fiber), Space and Planetary Science, Radio galaxy, Dynamic range, Scale structure, Astronomy, Astronomy and Astrophysics, Astrophysics, Very Long Baseline Array, Optical depth, Parsec
Abstract: We present a high dynamic range Very Long Baseline Array (VLBA) image of 3C 84 at 1.3 GHz. With these observations we have discovered a previously undetected component that is centered ~65 mas to the south of the compact core and has a diameter of ~40 mas. The nucleus of 3C 84 thus displays radio emission without interruption from the core out to a total length of 01 (24 h-1 pc), which is clear evidence for activity of the central engine in the centuries preceding the latest large outburst in 1960. From the absence of significant emission to the north of the core we find that the free-free optical depth at 1.3 GHz is likely to be ≥3.7 at a projected distance of 3.5 h-1 pc.
Published: 1996

48. FSC 10214+4724: A Gravitationally Lensed, Hidden QSO

Author: R. C. Vermeulen, Robert W. Goodrich, Marshall H. Cohen, Patrick Ogle, Andre Martel, Joseph S. Miller, and H. D. Tran
Subjects: Physics, Space and Planetary Science, Astronomy and Astrophysics, Astrophysics, Emission spectrum, Polarization (waves), Galaxy
Abstract: We present polarimetric evidence that the extraordinarily luminous galaxy FSC 10214+4724 harbors a hidden QSO. In polarized flux we see broad emission lines of C III] λ1909, C IV λ1550, and Lyα/N V λ1240. The narrow emission lines that dominate the total flux spectrum are unpolarized. Recent images have indicated that FSC 10214+4724 is actually gravitationally lensed, and we find strong evidence for Mg II λ2800 absorption at z = 1.316 in the spectrum of the QSO and weaker evidence for a possible continuum and absorption system at z = 0.893. Both of these systems could represent galaxies that contribute to the lensing.
Published: 1996

49. Superluminal Motions: The First 100 Sources

Author: R. C. Vermeulen
Subjects: Physics, education.field_of_study, Superluminal motion, Population, Quasar, Astrophysics, Galaxy, Luminosity, Lorentz factor, symbols.namesake, symbols, Range (statistics), Source counts, education
Abstract: First results from a large homogeneous superluminal motion survey are presented. The data do not show compelling evidence for the existence of intrinsically different populations of galaxies, BL Lac objects, or quasars. β app in the range 1–5h −1 occur with roughly equal frequency; higher values, up to β app = 10h −1 are rather more scarce than appeared to be the case from earlier work, which evidently concentrated on sources which are not representative of the general population. The β app distribution suggests that there might be a skewed distribution of Lorentz factors over the sample, with a peak at γb ≈ 2h −1 and a tail up to at least γb ≈ 10h −1. There appears to be a clearly rising upper envelope to the β app distribution when plotted as a function of observed 5 GHz luminosity; a combination of source counts and the apparent velocity statistics in a larger sample could provide much insight into the properties of radio jet sources.
Published: 1996

50. Simultaneous Multi-Frequency Imaging of the Nucleus of NGC 1275

Author: R. C. Vermeulen, Jonathan D. Romney, Vivek Dhawan, R. C. Walker, and K. I. Kellermann
Subjects: Physics, medicine.anatomical_structure, Feature (computer vision), Very-long-baseline interferometry, medicine, Astrophysics, Nucleus, Structural monitoring
Abstract: An unusual counterjet feature was discovered in 3C 84, the compact radio nucleus of NGC 1275, in the “First Science” observations on the VLBA at 8.4 GHz (Walker et al., 1994), and simultaneously in Global VLBI observations at 22 GHz (Vermeulen et al., 1994). Comparison of these images indicated a strongly inverted spectrum in this feature, but the interpretation was clouded by the two-year difference between the epochs of observation. To resolve this ambiguity, and to study the spectrum of the counterjet, we exploited the capabilities of the VLBA to make nearly simultaneous observations of 3C 84 at 2.3, 5.0, 8.4, 15.4, 22, and 43 GHz, in four apparitions over a 16-day period in January 1995. These observations also served to continue structural monitoring programs at 15 and 22 GHz. This paper presents preliminary images from those observations. A companion contribution by Walker et al. (1995) discusses the interpretation of the images.
Published: 1996

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