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1. Diffuse radio emission from non- Planck galaxy clusters in the LoTSS-DR2 fields

Author: D. N. Hoang, M. Brüggen, A. Botteon, T. W. Shimwell, X. Zhang, A. Bonafede, L. Bruno, E. Bonnassieux, R. Cassano, V. Cuciti, A. Drabent, F. de Gasperin, F. Gastaldello, G. Di Gennaro, M. Hoeft, A. Jones, G. V. Pignataro, H. J. A. Röttgering, A. Simionescu, R. J. van Weeren, D. N. Hoang, M. Br??ggen, A. Botteon, T. W. Shimwell, X. Zhang, A. Bonafede, L. Bruno, E. Bonnassieux, R. Cassano, V. Cuciti, A. Drabent, F. de Gasperin, F. Gastaldello, G. Di Gennaro, M. Hoeft, A. Jone, G. V. Pignataro, H. J. A. R??ttgering, A. Simionescu, and R. J. van Weeren
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, galaxie, radiation mechanism, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, X-ray, non-thermal, Space and Planetary Science, general, large-scale structure of Universe, clusters, Astrophysics - High Energy Astrophysical Phenomena, cluster, intracluster medium, Astrophysics::Galaxy Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Context.The presence of large-scale magnetic fields and ultra-relativistic electrons in the intra-cluster medium (ICM) is confirmed through the detection of diffuse radio synchrotron sources, so-called radio halos and relics. Due to their steep-spectrum nature, these sources are rarely detected at frequencies above a few gigahertz, especially in low-mass systems.Aims.The aim of this study is to discover and characterise diffuse radio sources in low-mass galaxy clusters in order to understand their origin and their scaling with host cluster properties.Methods.We searched for cluster-scale radio emission from low-mass galaxy clusters in the Low Frequency Array (LOFAR) Two-metre Sky Survey – Data Release 2 (LoTSS-DR2) fields. We made use of existing optical (Abell, DESI, WHL) and X-ray (comPRASS, MCXC) catalogues. The LoTSS-DR2 data were processed further to improve the quality of the images that are used to detect and characterise diffuse sources.Results.We detect diffuse radio emission in 28 galaxy clusters. The numbers of confirmed (candidates) halos and relics are six (seven) and 10 (three), respectively. Among these, 11 halos and 10 relics, including candidates, are newly discovered by LOFAR. In addition to these, five diffuse sources are detected in tailed radio galaxies and are probably associated with mergers during the formation of the host clusters. We are unable to classify a further 13 diffuse sources. We compare our newly detected, diffuse sources to known sources by placing them on the scaling relation between the radio power and the mass of the host clusters.
Published: 2022

2. Radio fossils, relics, and haloes in Abell 3266: cluster archaeology with ASKAP-EMU and the ATCA

Author: C J Riseley, E Bonnassieux, T Vernstrom, T J Galvin, A Chokshi, A Botteon, K Rajpurohit, S W Duchesne, A Bonafede, L Rudnick, M Hoeft, B Quici, D Eckert, M Brienza, C Tasse, E Carretti, J D Collier, J M Diego, L Di Mascolo, A M Hopkins, M Johnston-Hollitt, R R Keel, B S Koribalski, T H Reiprich, Australian Government, CSIRO Land and Water (Australia), Science and Industry Endowment Fund (Australia), European Research Council, European Commission, Netherlands Organization for Scientific Research, Ministerio de Ciencia, Innovación y Universidades (España), Agencia Estatal de Investigación (España), Australian Research Council, Department of Energy (US), Ministerio de Educación y Ciencia (España), Science and Technology Facilities Council (UK), University of Illinois, Higher Education Funding Council for England, Kavli Institute for Particle Astrophysics and Cosmology, The Ohio State University, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico (Brasil), Ministério da Ciência, Tecnologia e Inovação (Brasil), and German Research Foundation
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Galaxies: clusters: individual: Abell 3266, Astrophysics - astrophysics of galaxies, Astrophysics - cosmology and nongalactic astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, X-rays - galaxies - clusters, Galaxies - clusters - general: Galaxies - clusters - individual, Space and Planetary Science, X-rays: galaxies: clusters, Abell 3266, Astrophysics of Galaxies (astro-ph.GA), Galaxies: clusters: general, Galaxies: clusters: intracluster medium, Galaxies - clusters - intracluster medium
Abstract: Abell 3266 is a massive and complex merging galaxy cluster that exhibits significant substructure. We present new, highly sensitive radio continuum observations of Abell 3266 performed with the Australian Square Kilometre Array Pathfinder (0.8–1.1 GHz) and the Australia Telescope Compact Array (1.1–3.1 GHz). These deep observations provide new insights into recently reported diffuse non-thermal phenomena associated with the intracluster medium, including a ‘wrong-way’ relic, a fossil plasma source, and an as-yet unclassified central diffuse ridge, which we reveal comprises the brightest part of a large-scale radio halo detected here for the first time. The ‘wrong-way’ relic is highly atypical of its kind: it exhibits many classical signatures of a shock-related radio relic, while at the same time exhibiting strong spectral steepening. While radio relics are generally consistent with a quasi-stationary shock scenario, the ‘wrong-way’ relic is not. We study the spectral properties of the fossil plasma source; it exhibits an ultrasteep and highly curved radio spectrum, indicating an extremely aged electron population. The larger scale radio halo fills much of the cluster centre, and presents a strong connection between the thermal and non-thermal components of the intracluster medium, along with evidence of substructure. Whether the central diffuse ridge is simply a brighter component of the halo, or a mini-halo, remains an open question. Finally, we study the morphological and spectral properties of the multiple complex radio galaxies in this cluster in unprecedented detail, tracing their evolutionary history., The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. The Australian SKA Pathfinder is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) that is managed by CSIRO. Operation of ASKAP is funded by the Australian Government with support from the National Collaborative Research Infrastructure Strategy. ASKAP uses the resources of the Pawsey Supercomputing Centre. Establishment of ASKAP, the Murchison Radio-astronomy Observatory and the Pawsey Supercomputing Centre are initiatives of the Australian Government, with support from the Government of Western Australia and the Science and Industry Endowment Fund. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site., CJR, EB, and AB acknowledge financial support from the ERC Starting Grant ‘DRANOEL’, number 714245. A. Botteon acknowledges support from the VIDI research programme with project number 639.042.729, which is financed by the Netherlands Organisation for Scientific Research (NWO). KR and MB acknowledge financial support from the ERC Starting Grant ‘MAGCOW’, no. 714196. JMD acknowledges the support of projects PGC2018-101814-B-100 and María de Maeztu, ref. MDM-2017-0765. This research was supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. LDM is supported by the ERC-StG ‘ClustersXCosmo’ grant agreement 716762., This project used public archival data from the Dark Energy Survey (DES). Funding for the DES Projects has been provided by the US Department of Energy, the US National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Center for Cosmology and Astro-Particle Physics at the Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência, Tecnologia e Inovação, the Deutsche Forschungsgemeinschaft, and the Collaborating Institutions in the DES.
Published: 2022
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3. Deep low-frequency radio observations of Abell 2256

Author: K. Rajpurohit, E. Osinga, M. Brienza, A. Botteon, G. Brunetti, W. R. Forman, C. J. Riseley, F. Vazza, A. Bonafede, R. J. van Weeren, M. Brüggen, S. Rajpurohit, A. Drabent, D. Dallacasa, M. Rossetti, A. S. Rajpurohit, M. Hoeft, E. Bonnassieux, R. Cassano, and G. K. Miley
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Space and Planetary Science, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present the first detailed analysis of the radio halo in the merging galaxy cluster Abell 2256 using the LOFAR, uGMRT, and VLA. These observations combined with archival X-ray data allowed us to study the halo emission with unprecedented detail. The integrated radio emission from the entire halo is characterized by an ultra-steep spectrum, which can be described by a power law with $\alpha_{144 \rm MHz}^{1.5 \rm GHz}=-1.63\pm0.03$, and a radial steepening in the outer regions. The halo is significantly underluminous according to the scaling relations between radio power and mass at 1.4 GHz but not at 150 MHz; ultra-steep spectrum halos are predicted to be statistically underluminous. Despite the complex structure of this system, the radio halo morphology is remarkably similar to that of the X-ray emission. The radio surface brightness distribution across the halo is strongly correlated with the X-ray brightness of the intracluster medium. The derived correlations show sublinear slopes and there are distinct structures: the core is $\rm I_{R}\propto I_{X}^{1.51}$, the outermost region $\rm I_{R}\propto I_{X}^{0.41}$, and we find radio morphological connections with X-ray discontinuities. We also find a strong anti-correlation between the radio spectral index and the X-ray surface brightness, implying radial steepening. We suggests that the halo core is either related to old plasma from previous AGN activity, being advected, compressed and re-accelerated by mechanisms activated by the cold front or less turbulent with strong magnetic field in the core. The change in the radio vs X-ray correlation slopes in the outer regions of the halo could be due to a radial decline of magnetic field, increase in the number density of seed particles or increasing turbulence. Our findings suggest that that the emitting volume is not homogenous according to turbulence re-acceleration models., Comment: 19 pages, 15 figures, accepted for publication in A&A
Published: 2022

4. Deep low-frequency radio observations of Abell 2256 I: The filamentary radio relic

Author: K. Rajpurohit, R. J. van Weeren, M. Hoeft, F. Vazza, M. Brienza, W. Forman, D. Wittor, P. Domínguez-Fernández, S. Rajpurohit, C. J. Riseley, A. Botteon, E. Osinga, G. Brunetti, E. Bonnassieux, A. Bonafede, A. S. Rajpurohit, C. Stuardi, A. Drabent, M. Brüggen, D. Dallacasa, T. W. Shimwell, H. J. A. Röttgering, F. de Gasperin, G. K. Miley, M. Rossetti, Rajpurohit K., Van Weeren R.J., Hoeft M., Vazza F., Brienza M., Forman W., Wittor D., Dominguez-Fernandez P., Rajpurohit S., Riseley C.J., Botteon A., Osinga E., Brunetti G., Bonnassieux E., Bonafede A., Rajpurohit A.S., Stuardi C., Drabent A., Bruggen M., Dallacasa D., Shimwell T.W., Rottgering H.J.A., Gasperin F.D., Miley G.K., and Rossetti M.
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), FOS: Physical sciences, Astronomy and Astrophysics, Galaxy clusters, Galaxy cluster, Astrophysics::Cosmology and Extragalactic Astrophysics, Intracluster medium, Radio continuum emission, Space and Planetary Science, Large-scale structure of the universe, Astrophysics::Galaxy Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present deep and high fidelity images of the merging galaxy cluster Abell 2256 at low frequencies, using the upgraded Giant Metrewave Radio Telescope (uGMRT) and LOw-Frequency ARray (LOFAR). This cluster hosts one of the most prominent known relics, with a remarkably spectacular network of filamentary substructures. The new uGMRT (300-850 MHz) and LOFAR (120-169 MHz) observations, combined with the archival Karl G. Jansky Very Large Array (VLA; 1-4 GHz) data, allowed us to carry out the first spatially resolved spectral analysis of the exceptional relic emission down to 6 arcsec resolution over a broad range of frequencies. Our new sensitive radio images confirm the presence of complex filaments of magnetized relativistic plasma also at low frequencies. We find that the integrated spectrum of the relic is consistent with a single power law, without any sign of spectral steepening, at least below 3 GHz. Unlike previous claims, the relic shows an integrated spectral index of $-1.07\pm0.02$ between 144 MHz and 3 GHz, which is consistent with the (quasi)stationary shock approximation. The spatially resolved spectral analysis suggests that the relic surface very likely traces the complex shock front, with a broad distribution of Mach numbers propagating through a turbulent and dynamically active intracluster medium. Our results show that the northern part of the relic is seen edge-on and the southern part close to face-on. We suggest that the complex filaments are regions where higher Mach numbers dominate the (re-)acceleration of electrons that are responsible for the observed radio emission., Comment: 27 pages, 14 Figures, accepted for publication in ApJ
Published: 2021
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5. A 3.5 Mpc long radio relic in the galaxy cluster ClG 0217+70

Author: D. N. Hoang, X. Zhang, C. Stuardi, T. W. Shimwell, A. Bonafede, M. Brüggen, G. Brunetti, A. Botteon, R. Cassano, F. de Gasperin, G. Di Gennaro, M. Hoeft, H. Intema, K. Rajpurohit, H. J. A. Röttgering, A. Simionescu, R. J. van Weeren, Hoang D.N., Zhang X., Stuardi C., Shimwell T.W., Bonafede A., Bruggen M., Brunetti G., Botteon A., Cassano R., De Gasperin F., Di Gennaro G., Hoeft M., Intema H., Rajpurohit K., Rottgering H.J.A., Simionescu A., and Van Weeren R.J.
Subjects: Active galactic nucleus, Large-Scale Structure of Universe, Radiation mechanisms: non-thermal, Astrophysics::High Energy Astrophysical Phenomena, Radiation Mechanisms, ClG 0217+70, FOS: Physical sciences, Individual, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics-High Energy Astrophysical Phenomena, Clusters, Astrophysics-Astrophysics of Galaxies, X-rays, Galaxies: clusters: individual: ClG 0217+70, Surface brightness, Galaxy cluster, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Spectral index, Astronomy and Astrophysics, LOFAR, Galaxies, Astrophysics - Astrophysics of Galaxies, Galaxy, Non-Thermal, Radio halo, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), X-rays: galaxies: clusters, Intracluster Medium, Halo, Astrophysics - High Energy Astrophysical Phenomena, Galaxies: clusters: intracluster medium
Abstract: Context. Megaparsec-scale radio sources in the form of halos and relics are often detected in dynamically disturbed galaxy clusters. Although they are associated with merger-induced turbulence and shocks, respectively, their formation is not fully understood. Aims. We aim to identify the mechanisms responsible for particle acceleration and magnetic field amplification in the halo and relics of the galaxy cluster ClG 0217+70. Methods. We observed ClG 0217+70 with LOFAR at 141 MHz and with VLA at 1.5 GHz, and we combined these observations with VLA 1.4 GHz archival data to study the morphological and spectral properties of the diffuse sources. We added Chandra archival data to examine the thermal and non-thermal properties of the halo. Results. Our LOFAR and VLA data confirm the presence of a giant radio halo in the cluster centre and multiple relics in the outskirts. The radio and X-ray emission from the halo are correlated, implying a tight relation between the thermal and non-thermal components. The diffuse radio structure in the south-east, with a projected size of 3.5 Mpc, is the most extended radio relic detected to date. The spectral index across the relic width steepens towards the cluster centre, suggesting electron ageing in the post-shock regions. The shock Mach numbers for the relics derived from the spectral index map range between 2.0 and 3.2. However, the integrated spectral indices lead to increasingly high Mach numbers for the relics farther from the cluster centre. This discrepancy could be because the relation between injection and integrated spectra does not hold for distant shocks, suggesting that the cooling time for the radio-emitting electrons is longer than the crossing time of the shocks. The variations in the surface brightness of the relics and the low Mach numbers imply that the radio-emitting electrons are re-accelerated from fossil plasma that could originate in active galactic nuclei.
Published: 2021

6. The galaxy population within the virial radius of the Perseus cluster

Author: R. Mauersberger, Helmut Meusinger, M. Hoeft, Bringfried Stecklum, Daniel Apai, and C. Rudolf
Subjects: Physics, Supermassive black hole, Active galactic nucleus, 010308 nuclear & particles physics, FOS: Physical sciences, Astronomy and Astrophysics, Virial mass, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Astrophysics - Astrophysics of Galaxies, Redshift, Galaxy, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), 0103 physical sciences, Surface brightness, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, Luminosity function (astronomy)
Abstract: We investigate the galaxy population in a field of the Perseus cluster that roughly covers the virial radius of the cluster. The galaxies were selected on Schmidt CCD images in B and H alpha in combination with SDSS images. We present a catalogue of 1294 galaxies. Morphological information was obtained for 90% of the galaxies from the `eyeball' inspection, partly supported by the surface brightness profile analysis. Redshifts were taken from SDSS, literature sources, and own spectroscopic observations and are available for 24% of the catalogues galaxies. The galaxy catalogue is used to derive cluster properties, such as radial profiles, indications of sub-structure, virial mass, and viral radius and to study the cluster galaxy population with regard to morphological types and peculiarities, star formation rates and active galactic nuclei. In addition to the statistical approach, we present brief individual descriptions of 18 cluster galaxies with conspicuous morphological peculiarities. (Abstract modified to match the arXiv format.), Comment: Accepted for publication in A&A
Published: 2020
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7. Cassiopeia A, Cygnus A, Taurus A, and Virgo A at ultra-low radio frequencies

Author: F. de Gasperin, J. Vink, J. P. McKean, A. Asgekar, I. Avruch, M. J. Bentum, R. Blaauw, A. Bonafede, J. W. Broderick, M. Brüggen, F. Breitling, W. N. Brouw, H. R. Butcher, B. Ciardi, V. Cuciti, M. de Vos, S. Duscha, J. Eislöffel, D. Engels, R. A. Fallows, T. M. O. Franzen, M. A. Garrett, A. W. Gunst, J. Hörandel, G. Heald, M. Hoeft, M. Iacobelli, L. V. E. Koopmans, A. Krankowski, P. Maat, G. Mann, M. Mevius, G. Miley, R. Morganti, A. Nelles, M. J. Norden, A. R. Offringa, E. Orrú, H. Paas, V. N. Pandey, M. Pandey-Pommier, R. Pekal, R. Pizzo, W. Reich, A. Rowlinson, H. J. A. Rottgering, D. J. Schwarz, A. Shulevski, O. Smirnov, C. Sobey, M. Soida, M. Steinmetz, M. Tagger, M. C. Toribio, A. van Ardenne, A. J. van der Horst, M. P. van Haarlem, R. J. van Weeren, C. Vocks, O. Wucknitz, P. Zarka, P. Zucca, Astronomy, Kapteyn Astronomical Institute, 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), 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 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), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), 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 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), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-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), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), De Gasperin F., Vink J., McKean J.P., Asgekar A., Avruch I., Bentum M.J., Blaauw R., Bonafede A., Broderick J.W., Bruggen M., Breitling F., Brouw W.N., Butcher H.R., Ciardi B., Cuciti V., De Vos M., Duscha S., Eisloffel J., Engels D., Fallows R.A., Franzen T.M.O., Garrett M.A., Gunst A.W., Horandel J., Heald G., Hoeft M., Iacobelli M., Koopmans L.V.E., Krankowski A., Maat P., Mann G., Mevius M., Miley G., Morganti R., Nelles A., Norden M.J., Offringa A.R., Orru E., Paas H., Pandey V.N., Pandey-Pommier M., Pekal R., Pizzo R., Reich W., Rowlinson A., Rottgering H.J.A., Schwarz D.J., Shulevski A., Smirnov O., Sobey C., Soida M., Steinmetz M., Tagger M., Toribio M.C., Van Ardenne A., Van Der Horst A.J., Van Haarlem M.P., Van Weeren R.J., Vocks C., Wucknitz O., Zarka P., Zucca P., High Energy Astrophys. & Astropart. Phys (API, FNWI), Gravitation and Astroparticle Physics Amsterdam, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES)
Subjects: Astronomy, media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, radio continuum: general, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, radio continuum, law.invention, Telescope, law, 0103 physical sciences, Angular resolution, [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], Surface brightness, 010306 general physics, Cygnus A, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, media_common, High Energy Astrophysical Phenomena (astro-ph.HE), [PHYS]Physics [physics], Physics, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, LOFAR, Astrophysics - Astrophysics of Galaxies, interferometric [techniques], Cassiopeia A, techniques: interferometric, 13. Climate action, Space and Planetary Science, Sky, general, Astrophysics of Galaxies (astro-ph.GA), interferometric, ddc:520, general [radio continuum], Radio frequency, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], techniques, general [ontinuum]
Abstract: The four persistent radio sources in the northern sky with the highest flux density at metre wavelengths are Cassiopeia A, Cygnus A, Taurus A, and Virgo A; collectively they are called the A-team. Their flux densities at ultra-low frequencies (, 7 pages, 2 figures, accepted A&A, online data on A&A website
Published: 2020

8. A galaxy cluster in the innermost Zone of Avoidance, close to the radio phoenix VLSS J2217.5+5943

Author: Gregory R. Zeimann, M. W. Ochmann, M. Hoeft, Dirk Froebrich, S. Bhagat, Wolfram Kollatschny, Gary J. Hill, and Helmut Meusinger
Subjects: Physics, Spectral index, Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, Zone of Avoidance, Astronomy and Astrophysics, Context (language use), Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Galactic plane, Galaxy, Redshift, Space and Planetary Science, QB460, 10. No inequality, Astrophysics::Galaxy Astrophysics, Galaxy cluster
Abstract: Context. Galaxy clusters grow via mergers with other clusters and groups. Extended regions of diffuse radio emission with a steep radio spectral index are thought to be indicators of such merger events. Extended radio sources with a significantly curved spectrum and a complex morphology have been found in several galaxy clusters. It has been proposed that these so-called radio phoenices are witnesses of cluster mergers and of the presence of active galactic nuclei prior to the merger. Shock fronts or turbulence induced by the mergers are believed to reenergize plasma emitted in the past active phase of a galaxy. Aims. The steep spectrum radio source VLSS J2217.5+5943 shows a complex filamentary morphology and a curved spectrum. Therefore, the source has previously been classified as a radio phoenix. However, no galaxy cluster associated with this radio source had confidently been detected until now because the source is located in the direction of the innermost zone of the Galactic plane at b = +2.4°, the innermost Zone of Avoidance (ZoA). The main aim of this work is to identify galaxies that are part of a cluster at the location of VLSS J2217.5+5943, determine their redshifts, and analyze their connection with the radio source. The confirmation of a cluster would corroborate the classification of the radio source as a radio phoenix and demonstrate that extended, diffuse radio sources are useful indicators of the presence of a galaxy cluster, in particular in the innermost ZoA. Methods. We analyzed archival observations in the near infrared and mid infrared (Spitzer) to select the galaxies in the immediate neighborhood of the radio source. A sample of 23 galaxies were selected as candidate cluster members. Furthermore, we carried out deep integral field spectroscopy covering 6450 to 10 500 Å with the red unit of the Hobby-Eberly Telescope second generation low resolution spectrograph (LRS2-R). We also reanalyzed archival GMRT observations at 325 and 610 MHz. Results. We selected 23 galaxies within a radius of 2.5 arcmin, centered on RA = 22h17m.5, Dec = +59° 43′ (J2000). Spectra were obtained for three of the brightest galaxies. For two galaxies we derived redshifts of z = 0.165 and z = 0.161, based on NaD absorption and TiO band heads. Their spectra correspond to E-type galaxies. Both galaxies are spatially associated with VLSS J2217.5+5943. The spectrum of the third galaxy, which is slightly farther from the radio source, indicates a LINER spectral type at z = 0.042. It is apparently a foreground galaxy with respect to the cluster we identified. Conclusions. VLSS J2217.5+5943 is associated with a massive galaxy cluster at redshift z = 0.163 ± .003, supporting its classification as a radio phoenix. The intrinsic properties of the radio source, computed for the cluster redshift, are in good agreement with those of other known radio phoenices. The identification of the galaxy cluster demonstrates that far-red spectroscopy with LRS2-R succeeds in determining the redshift of galaxies in the innermost ZoA. Moreover, it confirms that radio sources can be useful indicators of the presence of galaxy clusters in the ZoA.
Published: 2021

9. The 'Sausage' and 'Toothbrush' clusters of galaxies and the prospects of LOFAR observations of clusters of galaxies

Author: H. Röttgering, R. van Weeren, M. Brüggen, J. Croston, M. Hoeft, G. Ogrean, P. Barthel, P. Best, A. Bonafede, G. Brunetti, R. Cassano, K. Chyży, J. Conway, F. De Gasperin, C. Ferrari, G. Heald, N. Jackson, M. Jarvis, M. Lehnert, G. Macario, G. Miley, E. Orrú, R. Pizzo, D. Rafferty, A. Stroe, C. Tasse, S. van der Tol, G. White, M. Wise, and null on behalf of the LOFAR collaboratio
Subjects: Physics, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, LOFAR, 01 natural sciences, Galaxy, Redshift, Radio telescope, Galaxy groups and clusters, Space and Planetary Science, 0103 physical sciences, Cluster (physics), Ionosphere, 010306 general physics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Galaxy cluster
Abstract: LOFAR, the Low Frequency Radio Array, is a new pan-European radio telescope that is almost fully operational. One of its main drivers is to make deep images of the low frequency radio sky. To be able to do this a number of challenges need to be addressed. These include the high data rates, removal of radio frequency interference, calibration of the beams and correcting for the corrupting influence of the ionosphere. One of the key science goals is to study merger shocks, particle acceleration mechanisms and the structure of magnetic fields in nearby and distant merging clusters. Recent studies with the GMRT and WSRT radio telescopes of the "Sausage" and the "Toothbrush" clusters have given a very good demonstration of the power of radio observations to study merging clusters. Recently we discovered that both clusters contain relic and halo sources, large diffuse regions of radio emission not associated with individual galaxies. The 2 Mpc northern relic in the Sausage cluster displays highly aligned magnetic fields and and exhibits a strong spectral index gradient that is a consequence of cooling of the synchrotron emitting particles in the post-shock region. We have argued that these observations provide strong evidence that shocks in merging clusters are capable of accelerating particles. For the Toothbrush cluster we observe a puzzling linear relic that extends over 2 Mpc. The proposed scenario is that a triple-merger can lead to such a structure. With LOFAR's sensitivity it will not only be possible to trace much weaker shocks, but also to study those shocks due to merging clusters up to redshifts of at least one. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Published: 2013

10. Corrigendum: A large light-mass component of cosmic rays at 10

Author: S, Buitink, A, Corstanje, H, Falcke, J R, Hörandel, T, Huege, A, Nelles, J P, Rachen, L, Rossetto, P, Schellart, O, Scholten, S, Ter Veen, S, Thoudam, T N G, Trinh, J, Anderson, A, Asgekar, I M, Avruch, M E, Bell, M J, Bentum, G, Bernardi, P, Best, A, Bonafede, F, Breitling, J W, Broderick, W N, Brouw, M, Brüggen, H R, Butcher, D, Carbone, B, Ciardi, J E, Conway, F, de Gasperin, E, de Geus, A, Deller, R-J, Dettmar, G, van Diepen, S, Duscha, J, Eislöffel, D, Engels, J E, Enriquez, R A, Fallows, R, Fender, C, Ferrari, W, Frieswijk, M A, Garrett, J M, Grießmeier, A W, Gunst, M P, van Haarlem, T E, Hassall, G, Heald, J W T, Hessels, M, Hoeft, A, Horneffer, M, Iacobelli, H, Intema, E, Juette, A, Karastergiou, V I, Kondratiev, M, Kramer, M, Kuniyoshi, G, Kuper, J, van Leeuwen, G M, Loose, P, Maat, G, Mann, S, Markoff, R, McFadden, D, McKay-Bukowski, J P, McKean, M, Mevius, D D, Mulcahy, H, Munk, M J, Norden, E, Orru, H, Paas, M, Pandey-Pommier, V N, Pandey, M, Pietka, R, Pizzo, A G, Polatidis, W, Reich, H J A, Röttgering, A M M, Scaife, D J, Schwarz, M, Serylak, J, Sluman, O, Smirnov, B W, Stappers, M, Steinmetz, A, Stewart, J, Swinbank, M, Tagger, Y, Tang, C, Tasse, M C, Toribio, R, Vermeulen, C, Vocks, C, Vogt, R J, van Weeren, R A M J, Wijers, S J, Wijnholds, M W, Wise, O, Wucknitz, S, Yatawatta, P, Zarka, and J A, Zensus
Published: 2016

11. Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes (Corrigendum)

Author: C. Sotomayor-Beltran, C. Sobey, J. W. T. Hessels, G. de Bruyn, A. Noutsos, A. Alexov, J. Anderson, A. Asgekar, I. M. Avruch, R. Beck, M. E. Bell, M. R. Bell, M. J. Bentum, G. Bernardi, P. Best, L. Birzan, A. Bonafede, F. Breitling, J. Broderick, W. N. Brouw, M. Brüggen, B. Ciardi, F. de Gasperin, R.-J. Dettmar, A. van Duin, S. Duscha, J. Eislöffel, H. Falcke, R. A. Fallows, R. Fender, C. Ferrari, W. Frieswijk, M. A. Garrett, J. Grießmeier, T. Grit, A. W. Gunst, T. E. Hassall, G. Heald, M. Hoeft, A. Horneffer, M. Iacobelli, E. Juette, A. Karastergiou, E. Keane, J. Kohler, M. Kramer, V. I. Kondratiev, L. V. E. Koopmans, M. Kuniyoshi, G. Kuper, J. van Leeuwen, P. Maat, G. Macario, S. Markoff, J. P. McKean, D. D. Mulcahy, H. Munk, E. Orru, H. Paas, M. Pandey-Pommier, M. Pilia, R. Pizzo, A. G. Polatidis, W. Reich, H. Röttgering, M. Serylak, J. Sluman, B. W. Stappers, M. Tagger, Y. Tang, C. Tasse, S. ter Veen, R. Vermeulen, R. J. van Weeren, R. A. M. J. Wijers, S. J. Wijnholds, M. W. Wise, O. Wucknitz, S. Yatawatta, P. Zarka, Astronomisches Institut der Ruhr-Universität Bochum, Ruhr-Universität Bochum [Bochum], Max-Planck-Institut für Radioastronomie (MPIFR), Netherlands Institute for Radio Astronomy (ASTRON), School of Oceanography [Seattle], University of Washington [Seattle], SRON Netherlands Institute for Space Research (SRON), Université de Tours (UT), CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), University of Southampton, Max-Planck-Institut für Astrophysik (MPA), Max-Planck-Gesellschaft, Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), University of Edinburgh, Leiden Observatory [Leiden], Universiteit Leiden, Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Max Planck Institute for Astrophysics, Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Thüringer Landessternwarte Tautenburg (TLS), Institute of Mathematical and Physical Sciences, Department of Quantitative Methods, Università degli studi di Genova = University of Genoa (UniGe), 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), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], 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), Oxford Astrophysics, University of Oxford, Centre for Astrophysics and Supercomputing (Centre for Astrophysics and Supercomputing), Swinburne University of Technology [Melbourne], Hessisches Landesmuseum Darmstadt, Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), 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), Department of Physics-Electronics, Rhodes University, Grahamstown, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), SKA South Africa, Ska South Africa, Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, ANR-09-JCJC-0001,OPALES(2009), European Project: 224897,EC:FP7:PEOPLE,FP7-PEOPLE-2007-2-2-ERG,WIDEMAP(2008), Université de Tours, Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Pierre et Marie Curie - Paris 6 (UPMC), Universiteit Leiden [Leiden], Universita degli studi di Genova, 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], Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Harvard University [Cambridge]-Smithsonian Institution, and Smithsonian Institution-Harvard University [Cambridge]
Subjects: 010504 meteorology & atmospheric sciences, Astronomy, Astrophysics, Low frequency, 01 natural sciences, Radio telescope, symbols.namesake, Optics, 0103 physical sciences, Faraday effect, 010303 astronomy & astrophysics, GeneralLiterature_REFERENCE(e.g.,dictionaries,encyclopedias,glossaries), 0105 earth and related environmental sciences, Physics, polarization, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], business.industry, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, LOFAR, techniques: polarimetric, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics], symbols, business, addenda, errata
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: 2015

12. LOFAR sparse image reconstruction

Author: H. Garsden, J. N. Girard, J. L. Starck, S. Corbel, C. Tasse, A. Woiselle, J. P. McKean, A. S. van Amesfoort, J. Anderson, I. M. Avruch, R. Beck, M. J. Bentum, P. Best, F. Breitling, J. Broderick, M. Brüggen, H. R. Butcher, B. Ciardi, F. de Gasperin, E. de Geus, M. de Vos, S. Duscha, J. Eislöffel, D. Engels, H. Falcke, R. A. Fallows, R. Fender, C. Ferrari, W. Frieswijk, M. A. Garrett, J. Grießmeier, A. W. Gunst, T. E. Hassall, G. Heald, M. Hoeft, J. Hörandel, A. van der Horst, E. Juette, A. Karastergiou, V. I. Kondratiev, M. Kramer, M. Kuniyoshi, G. Kuper, G. Mann, S. Markoff, R. McFadden, D. McKay-Bukowski, D. D. Mulcahy, H. Munk, M. J. Norden, E. Orru, H. Paas, M. Pandey-Pommier, V. N. Pandey, G. Pietka, R. Pizzo, A. G. Polatidis, A. Renting, H. Röttgering, A. Rowlinson, D. Schwarz, J. Sluman, O. Smirnov, B. W. Stappers, M. Steinmetz, A. Stewart, J. Swinbank, M. Tagger, Y. Tang, S. Thoudam, C. Toribio, R. Vermeulen, C. Vocks, R. J. van Weeren, S. J. Wijnholds, M. W. Wise, O. Wucknitz, S. Yatawatta, P. Zarka, A. Zensus, 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), 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), SAGEM Défense Sécurité [Massy], Netherlands Institute for Radio Astronomy (ASTRON), Delft University of Technology (TU Delft), SRON Netherlands Institute for Space Research (SRON), University of Edinburgh, Leibniz-Institut für Astrophysik Potsdam (AIP), Universität Hamburg (UHH), University of Southampton, 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 Oulu, 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), ANR-10-LABX-0023,UnivEarthS,Earth - Planets - Universe: observation, modeling, transfer(2010), ANR-11-IDEX-0005,USPC,Université Sorbonne Paris Cité(2011), ANR-09-JCJC-0001,OPALES(2009), European Project: 228261,EC:FP7:ERC,ERC-2008-AdG,SPARSEASTRO(2009), 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 d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), 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), Rhodes University, SKA South Africa, Ska South Africa, 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), ANR-10-LABX-0023,Labex UnivEarthS, ANR-11-IDEX-0005-02 ,USPC : Projet Université Sorbonne Paris Cité,Initiatives d’excellence - Laboratoire d’excellence INFLAMEX, and ANR-09-JCJC-0001,OPALES,nOn-thermal Processes in gALaxy cluStErs(2009)
Subjects: Sparse image, Phased array, Computer science, Aperture synthesis, Astronomy, EWI-26158, ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION, FOS: Physical sciences, IR-96629, techniques: image processing, 02 engineering and technology, 01 natural sciences, methods: numerical, Radio telescope, symbols.namesake, 0103 physical sciences, 0202 electrical engineering, electronic engineering, information engineering, Angular resolution, GeneralLiterature_REFERENCE(e.g.,dictionaries,encyclopedias,glossaries), 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), METIS-312678, Sparse matrix, image processing [techniques], Astrophysics::Instrumentation and Methods for Astrophysics, numerical [methods], 020206 networking & telecommunications, Astronomy and Astrophysics, LOFAR, Inverse problem, interferometric [techniques], Interferometry, techniques: interferometric – methods: numerical – techniques: image processing, techniques: image, Compressed sensing, Fourier transform, Space and Planetary Science, [SDU]Sciences of the Universe [physics], techniques: interferometric, symbols, processing, Deconvolution, Astrophysics - Instrumentation and Methods for Astrophysics, Algorithm
Abstract: Context. The LOw Frequency ARray (LOFAR) radio telescope is a giant digital phased array interferometer with multiple antennas distributed in Europe. It provides discrete sets of Fourier components of the sky brightness. Recovering the original brightness distribution with aperture synthesis forms an inverse problem that can be solved by various deconvolution and minimization methods Aims. Recent papers have established a clear link between the discrete nature of radio interferometry measurement and the "compressed sensing" (CS) theory, which supports sparse reconstruction methods to form an image from the measured visibilities. Empowered by proximal theory, CS offers a sound framework for efficient global minimization and sparse data representation using fast algorithms. Combined with instrumental direction-dependent effects (DDE) in the scope of a real instrument, we developed and validated a new method based on this framework Methods. We implemented a sparse reconstruction method in the standard LOFAR imaging tool and compared the photometric and resolution performance of this new imager with that of CLEAN-based methods (CLEAN and MS-CLEAN) with simulated and real LOFAR data Results. We show that i) sparse reconstruction performs as well as CLEAN in recovering the flux of point sources; ii) performs much better on extended objects (the root mean square error is reduced by a factor of up to 10); and iii) provides a solution with an effective angular resolution 2-3 times better than the CLEAN images. Conclusions. Sparse recovery gives a correct photometry on high dynamic and wide-field images and improved realistic structures of extended sources (of simulated and real LOFAR datasets). This sparse reconstruction method is compatible with modern interferometric imagers that handle DDE corrections (A- and W-projections) required for current and future instruments such as LOFAR and SKA, Published in A&A, 19 pages, 9 figures
Published: 2015

13. The LOFAR Multifrequency Snapshot Sky Survey (MSSS): I. Survey description and first results

Author: G. H. Heald, R. F. Pizzo, E. Orrú, R. P. Breton, D. Carbone, C. Ferrari, M. J. Hardcastle, W. Jurusik, G. Macario, D. Mulcahy, D. Rafferty, A. Asgekar, M. Brentjens, R. A. Fallows, W. Frieswijk, M. C. Toribio, B. Adebahr, M. Arts, M. R. Bell, A. Bonafede, J. Bray, J. Broderick, T. Cantwell, P. Carroll, Y. Cendes, A. O. Clarke, J. Croston, S. Daiboo, F. de Gasperin, J. Gregson, J. Harwood, T. Hassall, V. Heesen, A. Horneffer, A. J. van der Horst, M. Iacobelli, V. Jelić, D. Jones, D. Kant, G. Kokotanekov, P. Martin, J. P. McKean, L. K. Morabito, B. Nikiel-Wroczyński, A. Offringa, V. N. Pandey, M. Pandey-Pommier, M. Pietka, L. Pratley, C. Riseley, A. Rowlinson, J. Sabater, A. M. M. Scaife, L. H. A. Scheers, K. Sendlinger, A. Shulevski, M. Sipior, C. Sobey, A. J. Stewart, A. Stroe, J. Swinbank, C. Tasse, J. Trüstedt, E. Varenius, S. van Velzen, N. Vilchez, R. J. van Weeren, S. Wijnholds, W. L. Williams, A. G. de Bruyn, R. Nijboer, M. Wise, A. Alexov, J. Anderson, I. M. Avruch, R. Beck, M. E. Bell, I. van Bemmel, M. J. Bentum, G. Bernardi, P. Best, F. Breitling, W. N. Brouw, M. Brüggen, H. R. Butcher, B. Ciardi, J. E. Conway, E. de Geus, A. de Jong, M. de Vos, A. Deller, R.-J. Dettmar, S. Duscha, J. Eislöffel, D. Engels, H. Falcke, R. Fender, M. A. Garrett, J. Grießmeier, A. W. Gunst, J. P. Hamaker, J. W. T. Hessels, M. Hoeft, J. Hörandel, H. A. Holties, H. Intema, N. J. Jackson, E. Jütte, A. Karastergiou, W. F. A. Klijn, V. I. Kondratiev, L. V. E. Koopmans, M. Kuniyoshi, G. Kuper, C. Law, J. van Leeuwen, M. Loose, P. Maat, S. Markoff, R. McFadden, D. McKay-Bukowski, M. Mevius, J. C. A. Miller-Jones, R. Morganti, H. Munk, A. Nelles, J. E. Noordam, M. J. Norden, H. Paas, A. G. Polatidis, W. Reich, A. Renting, H. Röttgering, A. Schoenmakers, D. Schwarz, J. Sluman, O. Smirnov, B. W. Stappers, M. Steinmetz, M. Tagger, Y. Tang, S. ter Veen, S. Thoudam, R. Vermeulen, C. Vocks, C. Vogt, R. A. M. J. Wijers, O. Wucknitz, S. Yatawatta, P. Zarka, Heald, G.H., Pizzo, R.F., Orrú, E., Breton, R.P., Carbone, D., Ferrari, C., Hardcastle, M.J., Jurusik, W., Macario, G., Mulcahy, D., Rafferty, D., Asgekar, A., Brentjens, M., Fallows, R.A., Frieswijk, W., Toribio, M.C., Adebahr, B., Arts, M., Bell, M.R., Bonafede, A., Bray, J., Broderick, J., Cantwell, T., Carroll, P., Cendes, Y., Clarke, A.O., Croston, J., Daiboo, S., De Gasperin, F., Gregson, J., Harwood, J., Hassall, T., Heesen, V., Horneffer, A., Van Der Horst, A.J., Iacobelli, M., Jelić, V., Jones, D., Kant, D., Kokotanekov, G., Martin, P., McKean, J.P., Morabito, L.K., Nikiel-Wroczyński, B., Offringa, A., Pandey, V.N., Pandey-Pommier, M., Pietka, M., Pratley, L., Riseley, C., Rowlinson, A., Sabater, J., Scaife, A.M.M., Scheers, L.H.A., Sendlinger, K., Shulevski, A., Sipior, M., Sobey, C., Stewart, A.J., Stroe, A., Swinbank, J., Tasse, C., Trüstedt, J., Varenius, E., Van Velzen, S., Vilchez, N., Van Weeren, R.J., Wijnholds, S., Williams, W.L., De Bruyn, A.G., Nijboer, R., Wise, M., Alexov, A., Anderson, J., Avruch, I.M., Beck, R., Bell, M.E., Van Bemmel, I., Bentum, M.J., Bernardi, G., Best, P., Breitling, F., Brouw, W.N., Brüggen, M., Butcher, H.R., Ciardi, B., Conway, J.E., De Geus, E., De Jong, A., De Vos, M., Deller, A., Dettmar, R.-J., Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Fender, R., Garrett, M.A., Grießmeier, J., Gunst, A.W., Hamaker, J.P., Hessels, J.W.T., Hoeft, M., Hörandel, J., Holties, H.A., Intema, H., Jackson, N.J., Jütte, E., Karastergiou, A., Klijn, W.F.A., Kondratiev, V.I., Koopmans, L.V.E., Kuniyoshi, M., Kuper, G., Law, C., Van Leeuwen, J., Loose, M., Maat, P., Markoff, S., McFadden, R., McKay-Bukowski, D., Mevius, M., Miller-Jones, J.C.A., Morganti, R., Munk, H., Nelles, A., Noordam, J.E., Norden, M.J., Paas, H., Polatidis, A.G., Reich, W., Renting, A., Röttgering, H., Schoenmakers, A., Schwarz, D., Sluman, J., Smirnov, O., Stappers, B.W., Steinmetz, M., Tagger, M., Tang, Y., Ter Veen, S., Thoudam, S., Vermeulen, R., Vocks, C., Vogt, C., Wijers, R.A.M.J., Wucknitz, O., Yatawatta, S., Zarka, P., High Energy Astrophys. & Astropart. Phys (API, FNWI), Netherlands Institute for Radio Astronomy (ASTRON), Jodrell Bank Centre for Astrophysics (JBCA), University of Manchester [Manchester], University of Hertfordshire [Hatfield] (UH), Uniwersytet Jagielloński w Krakowie = Jagiellonian University (UJ), Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), University of Southampton, Jacobs University [Bremen], Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), 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), Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), School of Physics and Astronomy [Southampton], Leiden Observatory, Leiden University (Leiden Observatory), 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), Max-Planck-Institut für Radioastronomie (MPIFR), Laboratory for Atmospheric and Space Physics [Boulder] (LASP), University of Colorado [Boulder], Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), 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)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, Leiden Observatory [Leiden], Universiteit Leiden, SRON Netherlands Institute for Space Research (SRON), Leibniz-Institut für Astrophysik Potsdam (AIP), Research School of Astronomy and Astrophysics [Canberra] (RSAA), Australian National University (ANU), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Los Alamos National Laboratory (LANL), Astronomisches Institut der Ruhr-Universität Bochum, Ruhr-Universität Bochum [Bochum], Thüringer Landessternwarte Tautenburg (TLS), Radboud University [Nijmegen], 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), Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), ANR-09-JCJC-0001,OPALES(2009), European Project: 247295,EC:FP7:ERC,ERC-2009-AdG,AARTFAAC(2010), European Project: 267697,EC:FP7:ERC,ERC-2010-AdG_20100224,4PI-SKY(2011), ITA, GBR, FRA, DEU, NLD, 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), Centre d'études européennes et de politique comparée (CEE), Sciences Po (Sciences Po)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Harvard University [Cambridge]-Smithsonian Institution, Universiteit Leiden [Leiden], 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), 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), Astronomy, Kapteyn Astronomical Institute, Jodrell Bank Centre for Astrophysics, Jagiellonian University [Krakow] (UJ), 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), 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)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Smithsonian Institution-Harvard University [Cambridge], Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), ANR-09-JCJC-0001,OPALES,nOn-thermal Processes in gALaxy cluStErs(2009), and Database Architectures
Subjects: 010504 meteorology & atmospheric sciences, Computer science, Astronomy, media_common.quotation_subject, FOS: Physical sciences, METIS-315082, 01 natural sciences, Radio spectrum, Radio continuum: general, surveys, 0103 physical sciences, radio continuum: general, Survey, GeneralLiterature_REFERENCE(e.g.,dictionaries,encyclopedias,glossaries), 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 0105 earth and related environmental sciences, Remote sensing, media_common, Giant Metrewave Radio Telescope, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, Square kilometre array, IR-98663, Sky, [SDU]Sciences of the Universe [physics], Space and Planetary Science, Experimental High Energy Physics, EWI-26540, Snapshot (computer storage), general [radio continuum], Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: We present the Multifrequency Snapshot Sky Survey (MSSS), the first northern-sky LOFAR imaging survey. In this introductory paper, we first describe in detail the motivation and design of the survey. Compared to previous radio surveys, MSSS is exceptional due to its intrinsic multifrequency nature providing information about the spectral properties of the detected sources over more than two octaves (from 30 to 160 MHz). The broadband frequency coverage, together with the fast survey speed generated by LOFAR's multibeaming capabilities, make MSSS the first survey of the sort anticipated to be carried out with the forthcoming Square Kilometre Array (SKA). Two of the sixteen frequency bands included in the survey were chosen to exactly overlap the frequency coverage of large-area Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT) surveys at 74 MHz and 151 MHz respectively. The survey performance is illustrated within the "MSSS Verification Field" (MVF), a region of 100 square degrees centered at J2000 (RA,Dec)=(15h,69deg). The MSSS results from the MVF are compared with previous radio survey catalogs. We assess the flux and astrometric uncertainties in the catalog, as well as the completeness and reliability considering our source finding strategy. We determine the 90% completeness levels within the MVF to be 100 mJy at 135 MHz with 108" resolution, and 550 mJy at 50 MHz with 166" resolution. Images and catalogs for the full survey, expected to contain 150,000-200,000 sources, will be released to a public web server. We outline the plans for the ongoing production of the final survey products, and the ultimate public release of images and source catalogs., Comment: 23 pages, 19 figures. Accepted for publication in Astronomy & Astrophysics. MSSS Verification Field images and catalog data may be downloaded from http://vo.astron.nl
Published: 2015

14. Feedback in Active Galactic Nucleus Heating of Galaxy Clusters

Author: M. Brueggen and M. Hoeft
Subjects: Physics, Range (particle radiation), Astrophysics::High Energy Astrophysical Phenomena, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Thermal conduction, Luminosity, Accretion rate, Space and Planetary Science, Intracluster medium, Radiative transfer, Cluster (physics), Astrophysics::Galaxy Astrophysics, Galaxy cluster
Abstract: One of the challenges that models of AGN heating of the intracluster medium (ICM) face, is the question how the mechanical luminosity of the AGN is tuned to the radiative losses of the ICM. Here we implement a simple 1D model of a feedback mechanism that links the luminosity of the AGN to the accretion rate. We demonstrate how this simple feedback mechanism leads to a quasi-steady state for a broad range of parameters. Moreover, within this feedback model, we investigate the effect of thermal conduction and find that its relative importance depends strongly on the cluster mass.
Published: 2004

15. The Scale‐dependent Energy Transfer Rate as a Tracer for Star Formation in CosmologicalN‐Body Simulations

Author: M. Hoeft, J. P. Mücket, and P. Heide
Subjects: Physics, Structure formation, Star formation, Astrophysics (astro-ph), Dark matter, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Kinetic energy, Redshift, Computational physics, Interstellar medium, Supernova, Space and Planetary Science, Energy source
Abstract: We investigate the energy release due to the large-scale structure formation and the subsequent transfer of energy from larger to smaller scales. We calculate the power spectra for the large-scale velocity field and show that the coupling of modes results in a transfer of power predominately from larger to smaller scales. We use the concept of cumulative energy for calculating which energy amount is deposited into the small scales during the cosmological structure evolution. To estimate the contribution due to the gravitational interaction only we perform our investigations by means of dark matter simulations. The global mean of the energy transfer increases with redshift $\sim (z+1)^{3}$; this can be traced back to the similar evolution of the merging rates of dark matter halos. The global mean energy transfer can be decomposed into its local contributions, which allows to determine the energy injection per mass into a local volume. The obtained energy injection rates are at least comparable with other energy sources driving the interstellar turbulence as, e.g. by the supernova kinetic feedback. On that basis we make the crude assumption that processes causing this energy transfer from large to small scales, e.g. the merging of halos, may contribute substantially to drive the ISM turbulence which may eventually result in star formation on much smaller scales. We propose that the ratio of the local energy injection rate to the energy already stored within small-scale motions is a rough measure for the probability of the local star formation efficiency applicable within cosmological large-scale n-body simulations., 12 pages, 9 figures, accepted for publication in ApJ
Published: 2002

16. Enhancement of the electron screening effect for d + d fusion reactions in metallic environments

Author: M. Hoeft, P. Heide, G. Ruprecht, K. Czerski, A. Huke, and A. Biller
Subjects: Nuclear reaction, Materials science, Deuterium, Screening effect, General Physics and Astronomy, Nuclear fusion, Electron, Atomic physics, Order of magnitude, Charged particle, Beam (structure)
Abstract: To study the electron screening of nuclear reactions in metallic environments, angular distributions and thick target yields of the fusion reactions 2H(d,p)3H and 2H(d,n)3He have been measured on deuterons implanted in three different metal targets (Al, Zr and Ta) for beam energies ranging from 5 to 60 keV. The experimentally determined values of the screening energy are about one order of magnitude larger than the value achieved in a gas target experiment and significantly larger than the theoretical predictions. A clear target material dependence of the screening energy has been established.
Published: 2001

17. LOFAR: The LOw-Frequency ARray

Author: M. P. van Haarlem, M. W. Wise, A. W. Gunst, G. Heald, J. P. McKean, J. W. T. Hessels, A. G. de Bruyn, R. Nijboer, J. Swinbank, R. Fallows, M. Brentjens, A. Nelles, R. Beck, H. Falcke, R. Fender, J. Hörandel, L. V. E. Koopmans, G. Mann, G. Miley, H. Röttgering, B. W. Stappers, R. A. M. J. Wijers, S. Zaroubi, M. van den Akker, A. Alexov, J. Anderson, K. Anderson, A. van Ardenne, M. Arts, A. Asgekar, I. M. Avruch, F. Batejat, L. Bähren, M. E. Bell, M. R. Bell, I. van Bemmel, P. Bennema, M. J. Bentum, G. Bernardi, P. Best, L. Bîrzan, A. Bonafede, A.-J. Boonstra, R. Braun, J. Bregman, F. Breitling, R. H. van de Brink, J. Broderick, P. C. Broekema, W. N. Brouw, M. Brüggen, H. R. Butcher, W. van Cappellen, B. Ciardi, T. Coenen, J. Conway, A. Coolen, A. Corstanje, S. Damstra, O. Davies, A. T. Deller, R.-J. Dettmar, G. van Diepen, K. Dijkstra, P. Donker, A. Doorduin, J. Dromer, M. Drost, A. van Duin, J. Eislöffel, J. van Enst, C. Ferrari, W. Frieswijk, H. Gankema, M. A. Garrett, F. de Gasperin, M. Gerbers, E. de Geus, J.-M. Grießmeier, T. Grit, P. Gruppen, J. P. Hamaker, T. Hassall, M. Hoeft, H. A. Holties, A. Horneffer, A. van der Horst, A. van Houwelingen, A. Huijgen, M. Iacobelli, H. Intema, N. Jackson, V. Jelic, A. de Jong, E. Juette, D. Kant, A. Karastergiou, A. Koers, H. Kollen, V. I. Kondratiev, E. Kooistra, Y. Koopman, A. Koster, M. Kuniyoshi, M. Kramer, G. Kuper, P. Lambropoulos, C. Law, J. van Leeuwen, J. Lemaitre, M. Loose, P. Maat, G. Macario, S. Markoff, J. Masters, R. A. McFadden, D. McKay-Bukowski, H. Meijering, H. Meulman, M. Mevius, E. Middelberg, R. Millenaar, J. C. A. Miller-Jones, R. N. Mohan, J. D. Mol, J. Morawietz, R. Morganti, D. D. Mulcahy, E. Mulder, H. Munk, L. Nieuwenhuis, R. van Nieuwpoort, J. E. Noordam, M. Norden, A. Noutsos, A. R. Offringa, H. Olofsson, A. Omar, E. Orrú, R. Overeem, H. Paas, M. Pandey-Pommier, V. N. Pandey, R. Pizzo, A. Polatidis, D. Rafferty, S. Rawlings, W. Reich, J.-P. de Reijer, J. Reitsma, G. A. Renting, P. Riemers, E. Rol, J. W. Romein, J. Roosjen, M. Ruiter, A. Scaife, K. van der Schaaf, B. Scheers, P. Schellart, A. Schoenmakers, G. Schoonderbeek, M. Serylak, A. Shulevski, J. Sluman, O. Smirnov, C. Sobey, H. Spreeuw, M. Steinmetz, C. G. M. Sterks, H.-J. Stiepel, K. Stuurwold, M. Tagger, Y. Tang, C. Tasse, I. Thomas, S. Thoudam, M. C. Toribio, B. van der Tol, O. Usov, M. van Veelen, A.-J. van der Veen, S. ter Veen, J. P. W. Verbiest, R. Vermeulen, N. Vermaas, C. Vocks, C. Vogt, M. de Vos, E. van der Wal, R. van Weeren, H. Weggemans, P. Weltevrede, S. White, S. J. Wijnholds, T. Wilhelmsson, O. Wucknitz, S. Yatawatta, P. Zarka, A. Zensus, J. van Zwieten, Netherlands Institute for Radio Astronomy (ASTRON), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), Institute of Mathematical and Physical Sciences, Radboud university [Nijmegen], Laboratoire de Chimie Physique Moléculaire (LCPM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Max-Planck-Institut für Radioastronomie (MPIFR), University of Southampton, Leibniz-Institut für Astrophysik Potsdam (AIP), Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Medical Center Haaglanden, SRON Netherlands Institute for Space Research (SRON), University of Edinburgh, Jacobs University [Bremen], Technische Universität Dresden = Dresden University of Technology (TU Dresden), Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Department of Reproduction and Development, Erasmus University Rotterdam, London Institute for Mathematical Sciences, Netherlands Centre for Biodiversity, Leiden, The Netherlands, Thüringer Landessternwarte Tautenburg (TLS), Laboratoire Réactions et Génie des Procédés (LRGP), Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Medstar Research Institute, 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), Plant Research International, Business Unit Bioscience, Wageningen University and Research [Wageningen] (WUR), Dipartimento di Matematica 'Guido Castelnuovo' [Roma I] (Sapienza University of Rome), Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome], Centre de Mathématiques Laurent Schwartz (CMLS), Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X), Peuplements végétaux et bioagresseurs en milieu tropical (UMR PVBMT), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Université de La Réunion (UR), Ruhr-Universität Bochum [Bochum], Oxford Astrophysics, University of Oxford [Oxford], Amsterdam Center for Multiscale Modeling, Vrije Universiteit Amsterdam [Amsterdam] (VU), Vrije Universiteit Medical Centre (VUMC), Queen's Medical Centre, National Radio Astronomy Observatory (NRAO), University of Oulu, Department of Economics, Bryant University, Center for Agricultural Research in Suriname CELOS and Department of Biology, Anton de Kom Universiteit van Suriname - Anton de Kom University of Suriname [Paramaribo] (UVS), DLR Institute of Aerospace Medicine, Deutsches Zentrum für Luft- und Raumfahrt [Köln] (DLR), Onsala Space Observatory (OSO), Chalmers University of Technology [Göteborg], Geophysical Institute [Bergen] (GFI / BiU), University of Bergen (UiB), 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), Department of Astronomy and Astrophysics [PennState], Pennsylvania State University (Penn State), Penn State System-Penn State System, Academic Medical Center - Academisch Medisch Centrum [Amsterdam] (AMC), School of Physics and Astronomy [Southampton], 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), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Rhodes University, Grahamstown, Center for Information Technology CIT, Université de Groningen, Processus d'Activation Sélective par Transfert d'Energie Uni-électronique ou Radiatif (UMR 8640) (PASTEUR), Université Pierre et Marie Curie - Paris 6 (UPMC)-Département de Chimie - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut de Chimie du CNRS (INC)-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), Center for Operations and Econometrics, Center of Operation Research and Econometrics [Louvain] (CORE), Université Catholique de Louvain = Catholic University of Louvain (UCL)-Université Catholique de Louvain = Catholic University of Louvain (UCL), Finca El Encin, Instituto Madrileño de Investigación y Desarrollo Rural, Agrario y Alimentario (IMIDRA), Department of Surgery (EINDHOVEN - Surgery), Catharina Hospital, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Harvard-Smithsonian Center for Astrophysics (CfA), Smithsonian Institution-Harvard University [Cambridge], Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, ANR-09-JCJC-0001,OPALES(2009), Astronomy, KVI - Center for Advanced Radiation Technology, Radboud University [Nijmegen], Universiteit Leiden, Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome] (UNIROMA), École polytechnique (X)-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), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Harvard University-Smithsonian Institution, UMR Peuplement Végétaux et Bioagresseurs en Milieu Tropical (UMR PVBMT - INRA), Institut National de la Recherche Agronomique (INRA), 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), Technische Universität Dresden (TUD), university Rotterdam, 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)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Wageningen University and Research Centre [Wageningen] (WUR), Università degli Studi di Roma 'La Sapienza' [Rome], Department of Physics, University of Crete [Heraklion] (UOC), Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas (FORTH), Anton de Kom University of Suriname, Geophysical Institute [Bergen], University of Bergen (UIB), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Rhodes University, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris)-Centre National de la Recherche Scientifique (CNRS), SKA South Africa, Ska South Africa, Center for Operations and Econometrics, Universit´e catholique de Louvain and Fonds National de la Recherche Scientifique, Harvard University [Cambridge]-Smithsonian Institution, Observatoire de Paris - Site de Paris (OP), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS), ANR-09-JCJC-0001,OPALES,nOn-thermal Processes in gALaxy cluStErs(2009), High Energy Astrophys. & Astropart. Phys (API, FNWI), Van Haarlem, M.P., Wise, M.W., Gunst, A.W., Heald, G., McKean, J.P., Hessels, J.W.T., De Bruyn, A.G., Nijboer, R., Swinbank, J., Fallows, R., Brentjens, M., Nelles, A., Beck, R., Falcke, H., Fender, R., Hörandel, J., Koopmans, L.V.E., Mann, G., Miley, G., Röttgering, H., Stappers, B.W., Wijers, R.A.M.J., Zaroubi, S., Van Den Akker, M., Alexov, A., Anderson, J., Anderson, K., Van Ardenne, A., Arts, M., Asgekar, A., Avruch, I.M., Batejat, F., Bähren, L., Bell, M.E., Bell, M.R., Van Bemmel, I., Bennema, P., Bentum, M.J., Bernardi, G., Best, P., Bîrzan, L., Bonafede, A., Boonstra, A.-J., Braun, R., Bregman, J., Breitling, F., Van De Brink, R.H., Broderick, J., Broekema, P.C., Brouw, W.N., Brüggen, M., Butcher, H.R., Van Cappellen, W., Ciardi, B., Coenen, T., Conway, J., Coolen, A., Corstanje, A., Damstra, S., Davies, O., Deller, A.T., Dettmar, R.-J., Van Diepen, G., Dijkstra, K., Donker, P., Doorduin, A., Dromer, J., Drost, M., Van Duin, A., Eislöffel, J., Van Enst, J., Ferrari, C., Frieswijk, W., Gankema, H., Garrett, M.A., De Gasperin, F., Gerbers, M., De Geus, E., Grießmeier, J.-M., Grit, T., Gruppen, P., Hamaker, J.P., Hassall, T., Hoeft, M., Holties, H.A., Horneffer, A., Van Der Horst, A., Van Houwelingen, A., Huijgen, A., Iacobelli, M., Intema, H., Jackson, N., Jelic, V., De Jong, A., Juette, E., Kant, D., Karastergiou, A., Koers, A., Kollen, H., Kondratiev, V.I., Kooistra, E., Koopman, Y., Koster, A., Kuniyoshi, M., Kramer, M., Kuper, G., Lambropoulos, P., Law, C., Van Leeuwen, J., Lemaitre, J., Loose, M., Maat, P., Macario, G., Markoff, S., Masters, J., McFadden, R.A., McKay-Bukowski, D., Meijering, H., Meulman, H., Mevius, M., Middelberg, E., Millenaar, R., Miller-Jones, J.C.A., Mohan, R.N., Mol, J.D., Morawietz, J., Morganti, R., Mulcahy, D.D., Mulder, E., Munk, H., Nieuwenhuis, L., Van Nieuwpoort, R., Noordam, J.E., Norden, M., Noutsos, A., Offringa, A.R., Olofsson, H., Omar, A., Orrú, E., Overeem, R., Paas, H., Pandey-Pommier, M., Pandey, V.N., Pizzo, R., Polatidis, A., Rafferty, D., Rawlings, S., Reich, W., De Reijer, J.-P., Reitsma, J., Renting, G.A., Riemers, P., Rol, E., Romein, J.W., Roosjen, J., Ruiter, M., Scaife, A., Van Der Schaaf, K., Scheers, B., Schellart, P., Schoenmakers, A., Schoonderbeek, G., Serylak, M., Shulevski, A., Sluman, J., Smirnov, O., Sobey, C., Spreeuw, H., Steinmetz, M., Sterks, C.G.M., Stiepel, H.-J., Stuurwold, K., Tagger, M., Tang, Y., Tasse, C., Thomas, I., Thoudam, S., Toribio, M.C., Van Der Tol, B., Usov, O., Van Veelen, M., Van Der Veen, A.-J., Ter Veen, S., Verbiest, J.P.W., Vermeulen, R., Vermaas, N., Vocks, C., Vogt, C., De Vos, M., Van Der Wal, E., Van Weeren, R., Weggemans, H., Weltevrede, P., White, S., Wijnholds, S.J., Wilhelmsson, T., Wucknitz, O., Yatawatta, S., Zarka, P., Zensus, A., and Van Zwieten, J.
Subjects: instrumentation: interferometers -radio continuum: general -radio lines: general -dark ages, Computer science, Astronomy, INTERPLANETARY SCINTILLATION, radio continuum: general, 7. Clean energy, 01 natural sciences, Precision Array for Probing the Epoch of Reionization, law.invention, Observatory, law, first stars - telescopes, dark ages, instrumentation: interferometers, 010303 astronomy & astrophysics, Telescope, UNDERSTANDING RADIO POLARIMETRY, Instrumentation: Interferometer, SELF-CALIBRATION, Interferometry, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, reionization, Astrophysics - Instrumentation and Methods for Astrophysics, radio lines: general, first stars, Z-GREATER-THAN-5.7 QUASARS, FOS: Physical sciences, Murchison Widefield Array, 0103 physical sciences, RAY AIR-SHOWERS, Angular resolution, dark ages, reionization, first stars, Instrumentation and Methods for Astrophysics (astro-ph.IM), Remote sensing, 010308 nuclear & particles physics, telescopes, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, Sextant (astronomical), Dark ages, reionization, first star, Space and Planetary Science, [SDU]Sciences of the Universe [physics], PROBE WMAP OBSERVATIONS, DIGITAL SKY SURVEY, HIGH-REDSHIFT, MONTE-CARLO SIMULATIONS, INTERGALACTIC MEDIUM
Abstract: LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFAR covers the largely unexplored low-frequency range from 10-240 MHz and provides a number of unique observing capabilities. Spreading out from a core located near the village of Exloo in the northeast of the Netherlands, a total of 40 LOFAR stations are nearing completion. A further five stations have been deployed throughout Germany, and one station has been built in each of France, Sweden, and the UK. Digital beam-forming techniques make the LOFAR system agile and allow for rapid repointing of the telescope as well as the potential for multiple simultaneous observations. With its dense core array and long interferometric baselines, LOFAR achieves unparalleled sensitivity and angular resolution in the low-frequency radio regime. The LOFAR facilities are jointly operated by the International LOFAR Telescope (ILT) foundation, as an observatory open to the global astronomical community. LOFAR is one of the first radio observatories to feature automated processing pipelines to deliver fully calibrated science products to its user community. LOFAR's new capabilities, techniques and modus operandi make it an important pathfinder for the Square Kilometre Array (SKA). We give an overview of the LOFAR instrument, its major hardware and software components, and the core science objectives that have driven its design. In addition, we present a selection of new results from the commissioning phase of this new radio observatory., Comment: 56 pages, 34 figures, accepted for publication by A&A
Published: 2013
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18. First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256

Author: R. J. van Weeren, H. J. A. Röttgering, D. A. Rafferty, R. Pizzo, A. Bonafede, M. Brüggen, G. Brunetti, C. Ferrari, E. Orrù, G. Heald, J. P. McKean, C. Tasse, F. de Gasperin, L. Bîrzan, J. E. van Zwieten, S. van der Tol, A. Shulevski, N. Jackson, A. R. Offringa, J. Conway, H. T. Intema, T. E. Clarke, I. van Bemmel, G. K. Miley, G. J. White, M. Hoeft, R. Cassano, G. Macario, R. Morganti, M. W. Wise, C. Horellou, E. A. Valentijn, O. Wucknitz, K. Kuijken, T. A. Enßlin, J. Anderson, A. Asgekar, I. M. Avruch, R. Beck, M. E. Bell, M. R. Bell, M. J. Bentum, G. Bernardi, P. Best, A.-J. Boonstra, M. Brentjens, R. H. van de Brink, J. Broderick, W. N. Brouw, H. R. Butcher, W. van Cappellen, B. Ciardi, J. Eislöffel, H. Falcke, R. Fender, M. A. Garrett, M. Gerbers, A. Gunst, M. P. van Haarlem, J. P. Hamaker, T. Hassall, J. W. T. Hessels, L. V. E. Koopmans, G. Kuper, J. van Leeuwen, P. Maat, R. Millenaar, H. Munk, R. Nijboer, J. E. Noordam, V. N. Pandey, M. Pandey-Pommier, A. Polatidis, W. Reich, A. M. M. Scaife, A. Schoenmakers, J. Sluman, B. W. Stappers, M. Steinmetz, J. Swinbank, M. Tagger, Y. Tang, R. Vermeulen, M. de Vos, Astronomy, 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), Galaxies, Etoiles, Physique, Instrumentation (GEPI), 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), 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 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)-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), ANR-09-JCJC-0001,OPALES(2009), European Project: 224897,EC:FP7:PEOPLE,FP7-PEOPLE-2007-2-2-ERG,WIDEMAP(2008), 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), 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), Van Weeren, R.J., Röttgering, H.J.A., Rafferty, D.A., Pizzo, R., Bonafede, A., Brüggen, M., Brunetti, G., Ferrari, C., Orrù, E., Heald, G., McKean, J.P., Tasse, C., De Gasperin, F., Bîrzan, L., Van Zwieten, J.E., Van Der Tol, S., Shulevski, A., Jackson, N., Offringa, A.R., Conway, J., Intema, H.T., Clarke, T.E., Van Bemmel, I., Miley, G.K., White, G.J., Hoeft, M., Cassano, R., MacArio, G., Morganti, R., Wise, M.W., Horellou, C., Valentijn, E.A., Wucknitz, O., Kuijken, K., Enßlin, T.A., Anderson, J., Asgekar, A., Avruch, I.M., Beck, R., Bell, M.E., Bell, M.R., Bentum, M.J., Bernardi, G., Best, P., Boonstra, A.-J., Brentjens, M., Van De Brink, R.H., Broderick, J., Brouw, W.N., Butcher, H.R., Van Cappellen, W., Ciardi, B., Eislöffel, J., Falcke, H., Fender, R., Garrett, M.A., Gerbers, M., Gunst, A., Van Haarlem, M.P., Hamaker, J.P., Hassall, T., Hessels, J.W.T., Koopmans, L.V.E., Kuper, G., Van Leeuwen, J., Maat, P., Millenaar, R., Munk, H., Nijboer, R., Noordam, J.E., Pandey, V.N., Pandey-Pommier, M., Polatidis, A., Reich, W., Scaife, A.M.M., Schoenmakers, A., Sluman, J., Stappers, B.W., Steinmetz, M., Swinbank, J., Tagger, M., Tang, Y., Vermeulen, R., De Vos, M., and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: galaxies: clusters: individual: Abell 2256, Cosmology and Nongalactic Astrophysics (astro-ph.CO), PARTICLE-ACCELERATION, COMA CLUSTER, Astronomy, Astrophysics::High Energy Astrophysical Phenomena, ASTROPHYSICAL SHOCKS, radio continuum: general, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Radio spectrum, MAGNETIC-FIELDS, Relativistic particle, X-RAY-EMISSION, METIS-293218, 0103 physical sciences, MERGING GALAXY CLUSTER, EXTENDED RADIO-EMISSION, Telescope, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, Physics, [PHYS]Physics [physics], Spectral index, 010308 nuclear & particles physics, Astronomy and Astrophysics, telescopes, LOFAR, Astronomy and Astrophysic, EWI-22624, Galaxy, SHOCK ACCELERATION, DEEP 1.4 GHZ, Radio halo, Space and Planetary Science, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Halo, large-scale structure of Universe, IR-82401, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], SKY SURVEY, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Abell 2256 is one of the best known examples of a galaxy cluster hosting large-scale diffuse radio emission that is unrelated to individual galaxies. It contains both a giant radio halo and a relic, as well as a number of head-tail sources and smaller diffuse steep-spectrum radio sources. The origin of radio halos and relics is still being debated, but over the last years it has become clear that the presence of these radio sources is closely related to galaxy cluster merger events. Here we present the results from the first LOFAR Low band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our knowledge, the image presented in this paper at 63 MHz is the deepest ever obtained at frequencies below 100 MHz in general. Both the radio halo and the giant relic are detected in the image at 63 MHz, and the diffuse radio emission remains visible at frequencies as low as 20 MHz. The observations confirm the presence of a previously claimed ultra-steep spectrum source to the west of the cluster center with a spectral index of -2.3 \pm 0.4 between 63 and 153 MHz. The steep spectrum suggests that this source is an old part of a head-tail radio source in the cluster. For the radio relic we find an integrated spectral index of -0.81 \pm 0.03, after removing the flux contribution from the other sources. This is relatively flat which could indicate that the efficiency of particle acceleration at the shock substantially changed in the last \sim 0.1 Gyr due to an increase of the shock Mach number. In an alternative scenario, particles are re-accelerated by some mechanism in the downstream region of the shock, resulting in the relatively flat integrated radio spectrum. In the radio halo region we find indications of low-frequency spectral steepening which may suggest that relativistic particles are accelerated in a rather inhomogeneous turbulent region., Comment: 13 pages, 13 figures, accepted for publication in A\&A on April 12, 2012
Published: 2012

19. Wide-field LOFAR imaging of the field around the double-double radio galaxy B1834+620

Author: E. Orrù, S. van Velzen, R. F. Pizzo, S. Yatawatta, R. Paladino, M. Iacobelli, M. Murgia, H. Falcke, R. Morganti, A. G. de Bruyn, C. Ferrari, J. Anderson, A. Bonafede, D. Mulcahy, A. Asgekar, I. M. Avruch, R. Beck, M. E. Bell, I. van Bemmel, M. J. Bentum, G. Bernardi, P. Best, F. Breitling, J. W. Broderick, M. Brüggen, H. R. Butcher, B. Ciardi, J. E. Conway, A. Corstanje, E. de Geus, A. Deller, S. Duscha, J. Eislöffel, D. Engels, W. Frieswijk, M. A. Garrett, J. Grießmeier, A. W. Gunst, J. P. Hamaker, G. Heald, M. Hoeft, A. J. van der Horst, H. Intema, E. Juette, J. Kohler, V. I. Kondratiev, M. Kuniyoshi, G. Kuper, M. Loose, P. Maat, G. Mann, S. Markoff, R. McFadden, D. McKay-Bukowski, G. Miley, J. Moldon, G. Molenaar, H. Munk, A. Nelles, H. Paas, M. Pandey-Pommier, V. N. Pandey, G. Pietka, A. G. Polatidis, W. Reich, H. Röttgering, A. Rowlinson, A. Scaife, A. Schoenmakers, D. Schwarz, M. Serylak, A. Shulevski, O. Smirnov, M. Steinmetz, A. Stewart, J. Swinbank, M. Tagger, C. Tasse, S. Thoudam, M. C. Toribio, R. Vermeulen, C. Vocks, R. J. van Weeren, R. A. M. J. Wijers, M. W. Wise, O. Wucknitz, High Energy Astrophys. & Astropart. Phys (API, FNWI), Kapteyn Astronomical Institute, Astronomy, Orru, E., Van Velzen, S., Pizzo, R.F., Yatawatta, S., Paladino, R., Iacobelli, M., Murgia, M., Falcke, H., Morganti, R., De Bruyn, A.G., Ferrari, C., Anderson, J., Bonafede, A., Mulcahy, D., Asgekar, A., Avruch, I.M., Beck, R., Bell, M.E., Van Bemmel, I., Bentum, M.J., Bernardi, G., Best, P., Breitling, F., Broderick, J.W., Bruggen, M., Butcher, H.R., Ciardi, B., Conway, J.E., Corstanje, A., De Geus, E., Deller, A., Duscha, S., Eisloffel, J., Engels, D., Frieswijk, W., Garrett, M.A., Grießmeier, J., Gunst, A.W., Hamaker, J.P., Heald, G., Hoeft, M., Van Der Horst, A.J., Intema, H., Juette, E., Kohler, J., Kondratiev, V.I., Kuniyoshi, M., Kuper, G., Loose, M., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-BGBRowski, D., Miley, G., Moldon, J., Molenaar, G., Munk, H., Nelles, A., Paas, H., Pandey-Pommier, M., Pandey, V.N., Pietka, G., Polatidis, A.G., Reich, W., Rottgering, H., Rowlinson, A., Scaife, A., Schoenmakers, A., Schwarz, D., Serylak, M., Shulevski, A., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Tasse, C., Thoudam, S., Toribio, M.C., Vermeulen, R., Vocks, C., Van Weeren, R.J., Wijers, R.A.M.J., Wise, M.W., and Wucknitz, O.
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, interferometers [instrumentation], galaxies: active, Population, FOS: Physical sciences, Field of view, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astroparticle physic, Radio continuum: galaxie, 01 natural sciences, Instrumentation: interferometer, law.invention, Telescope, law, 0103 physical sciences, Bow shock (aerodynamics), instrumentation: interferometers, education, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, radio continuum: galaxies, Physics, education.field_of_study, Accretion (meteorology), 010308 nuclear & particles physics, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, radiation mechanisms: non-thermal, non-thermal [radiation mechanisms], Astrophysics - Astrophysics of Galaxies, galaxies [radio continuum], Redshift, interferometric [techniques], techniques: interferometric, astroparticle physics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), active [galaxies], Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The existence of double-double radio galaxies (DDRGs) is evidence for recurrent jet activity in AGN, as expected from standard accretion models. A detailed study of these rare sources provides new perspectives for investigating the AGN duty cycle, AGN-galaxy feedback, and accretion mechanisms. Large catalogues of radio sources provide statistical information about the evolution of the radio-loud AGN population out to high redshifts. Using wide-field imaging with the LOFAR telescope, we study both a well-known DDRG as well as a large number of radio sources in the field of view. We present a high resolution image of the DDRG B1834+620 obtained at 144 MHz using LOFAR commissioning data. Our image covers about 100 square degrees and contains over 1000 sources. The four components of the DDRG B1834+620 have been resolved for the first time at 144 MHz. Inner lobes were found to point towards the direction of the outer lobes, unlike standard FR~II sources. Polarized emission was detected in the northern outer lobe. The high spatial resolution allows the identification of a large number of small double-lobed radio sources; roughly 10% of all sources in the field are doubles with a separation smaller than 1 arcmin. The spectral fit of the four components is consistent with a scenario in which the outer lobes are still active or the jets recently switched off, while emission of the inner lobes is the result of a mix-up of new and old jet activity. From the presence of the newly extended features in the inner lobes of the DDRG, we can infer that the mechanism responsible for their formation is the bow shock that is driven by the newly launched jet. We find that the density of the small doubles exceeds the density of FR-II sources with similar properties at 1.4 GHz, but this difference becomes smaller for low flux densities., Comment: 13 pages, 8 figures, Accepted for publication in Astronomy & Astrophysics
Published: 2015

20. Training a team with simulated team members

Author: Raegan M. Hoeft, Martin van Schaik, A.M. Schaafstal, and TNO Technische Menskunde
Subjects: Teamwork, Engineering, Knowledge management, training, business.industry, Process (engineering), media_common.quotation_subject, Defence, Training (civil), teams, Task (project management), Medical Terminology, Human–computer interaction, business, Set (psychology), Team training, Medical Assisting and Transcription, media_common
Abstract: The process of training teams increasingly occurs in synthetic environments. However, it is often still modeled after live team training, including the disadvantages of live training, for example, the fact that all teammates must be available. This paper explores overcoming the disadvantages of human teammates in training teams in synthetic environments, while keeping the advantages of learning in a collaborative and cooperative fashion. Simulated teammates are a promising alternative because they are always available, may be modeled after experienced training personnel, and may be more cost effective in the long run. This paper details a research approach towards the definition of requirements for simulated teammates. In our approach, we carry out a set of experiments using confederates as simulated teammates, in a well-controlled simulation of a military command-and-control task The results of a first experiment show slightly better teamwork skills for those teams trained with simulated teammates.
Published: 2002

21. Simulations of magnetic fields in the cosmos.

Author: M. Hoeft
Published: 2006

22. Deep Very Large Array Observations of the Merging Cluster CIZA J2242.8+5301: Continuum and Spectral Imaging.

Author: G. Di Gennaro, R. J. van Weeren, M. Hoeft, H. Kang, D. Ryu, L. Rudnick, W. Forman, H. J. A. Röttgering, M. Brüggen, W. A. Dawson, N. Golovich, D. N. Hoang, H. T. Intema, C. Jones, R. P. Kraft, T. W. Shimwell, and A. Stroe
Subjects: STAR clusters, SPECTRAL imaging, SOLAR radio emission, ELECTROMAGNETIC waves
Abstract: Despite the progress that has been made in understanding radio relics, there are still open questions regarding the underlying particle acceleration mechanisms. In this paper, we present deep 1–4 GHz Very Large Array (VLA) observations of CIZA J2242.8+5301 (z = 0.1921), a double radio relic cluster characterized by small projection on the plane of the sky. Our VLA observations reveal, for the first time, the complex morphology of the diffuse sources and the filamentary structure of the northern relic. We discover new, faint, diffuse radio emission extending north of the main northern relic. Our Mach number estimates for the northern and southern relics, based on the radio spectral index map obtained using the VLA observations and existing LOw Frequency ARray (LOFAR) and Giant Metrewave Radio Telescope data, are consistent with previous radio and X-ray studies ( and ). However, color–color diagrams and models suggest a flatter injection spectral index than the one obtained from the spectral index map, indicating that projection effects might be not entirely negligible. The southern relic consists of five “arms.” Embedded in it, we find a tailed radio galaxy that seems to be connected to the relic. A spectral index flattening, where the radio tail connects to the relic, is also measured. We propose that the southern relic may trace AGN fossil electrons that are reaccelerated by a shock, with an estimated strength of . High-resolution mapping of other tailed radio galaxies also supports a scenario where AGN fossil electrons are revived by the merger event and could be related to the formation of some diffuse cluster radio emission. [ABSTRACT FROM AUTHOR]
Published: 2018
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23. Deep VLA Observations of the Cluster 1RXS J0603.3+4214 in the Frequency Range of 1–2 GHz.

Author: K. Rajpurohit, M. Hoeft, R. J. van Weeren, L. Rudnick, H. J. A. Röttgering, W. R. Forman, M. Brüggen, J. H. Croston, F. Andrade-Santos, W. A. Dawson, H. T. Intema, R. P. Kraft, C. Jones, and M. James Jee
Subjects: *GALACTIC halos, *VERY large array telescopes, *SURFACE brightness (Astronomy), *ASTRONOMICAL photometry, *RADIO telescopes, *MACH number
Abstract: We report L-band VLA observations of 1RXS J0603.3+4214, a cluster that hosts a bright radio relic, known as the Toothbrush, and an elongated giant radio halo. These new observations allow us to study the surface brightness distribution down to 1 arcsec resolution with very high sensitivity. Our images provide an unprecedented detailed view of the Toothbrush, revealing enigmatic filamentary structures. To study the spectral index distribution, we complement our analysis with published LOFAR and GMRT observations. The bright “brush” of the Toothbrush shows a prominent narrow ridge to its north with a sharp outer edge. The spectral index at the ridge is in the range −0.70 ≤ α ≤ −0.80. We suggest that the ridge is caused by projection along the line of sight. With a simple toy model for the smallest region of the ridge, we conclude that the magnetic field is below 5 μG and varies significantly across the shock front. Our model indicates that the actual Mach number is higher than that obtained from the injection index and agrees well with the one derived from the overall spectrum, namely . The radio halo shows an average spectral index of α = −1.16 ± 0.05 and a slight gradient from north to south. The southernmost part of the halo is steeper and possibly related to a shock front. Excluding the southernmost part, the halo morphology agrees very well with the X-ray morphology. A power-law correlation is found between the radio and X-ray surface brightness. [ABSTRACT FROM AUTHOR]
Published: 2018
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24. Merging the Worlds of Pets and Pills: Development and Evaluation of an Interprofessional Activity Linking Pharmacy and Veterinary Medicine.

Author: Hoeft M, Van Hooser J, Rupnow N, and Clarkson C
Abstract: Interprofessional education (IPE) is noticeably lacking between pharmacy and veterinary medicine students despite the two health professions overlapping in practice. To address this, an asynchronous IPE activity was developed together with practicing pharmacists and veterinarians. Students worked in groups across two campuses to discuss clinical cases, specifically requiring input from both professions. Students reported they learned more about the two professions' interconnection, felt prepared to interact with the other professionals in the future, and found value in learning from each other. Overall, the results of this study outline a successful pilot IPE activity between veterinary medicine and pharmacy students., Competing Interests: Conflict of InterestThe authors declare no competing interests., (© The Author(s) 2024.)
Published: 2024
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25. Validation of Bayesian design for broadband microslit panel absorbers using causal inference.

Author: Xiang N, Hoeft M, Fackler CJ, Chen Z, and Barach P
Abstract: This paper discusses experimental validations of multilayer microslit panels (MSPs) designed via Bayesian inference to obtain both high sound absorption and wide bandwidth simultaneously. Microslit perforation in thin panels is similar to microperforated panels [Xiang, Fackler, Hou, and Schmitt (2022). J. Acoust. Soc. Am. 151(5), 3094-3103]. MSP absorbers in single-layer configurations are functioning in a limited frequency range. By stacking the MSPs in multiple layered structures, absorbing performance may be widened in frequency ranges while retaining high absorption coefficients. Besides design challenges of multiple MSPs in layered structures to fulfill a practical requirement and minimize fabrication complexity, this paper further discusses challenges in experimental validations when experimental results undesirably deviate from the initial Bayesian design. Causation analysis is applied to the validation efforts where a causal model-based inference effectively provides causal reasoning of fabrication inaccuracies. Along with the causal inference, a causal reasoning conducted in this work can guide corrections due to fabrication inaccuracies during the iterative validation process., (© 2023 Acoustical Society of America.)
Published: 2023
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26. Wireless Link Selection Methods for Maritime Communication Access Networks-A Deep Learning Approach.

Author: Hoeft M, Gierlowski K, and Wozniak J
Subjects: Wireless Technology, Neural Networks, Computer, Communication, Computer Communication Networks, Deep Learning
Abstract: In recent years, we have been witnessing a growing interest in the subject of communication at sea. One of the promising solutions to enable widespread access to data transmission capabilities in coastal waters is the possibility of employing an on-shore wireless access infrastructure. However, such an infrastructure is a heterogeneous one, managed by many independent operators and utilizing a number of different communication technologies. If a moving sea vessel is to maintain a reliable communication within such a system, it needs to employ a set of network mechanisms dedicated for this purpose. In this paper, we provide a short overview of such requirements and overall characteristics of maritime communication, but our main focus is on the link selection procedure-an element of critical importance for the process of changing the device/system which the mobile vessel uses to retain communication with on-shore networks. The paper presents the concept of employing deep neural networks for the purpose of link selection. The proposed methods have been verified using propagation models dedicated to realistically represent the environment of maritime communications and compared to a number of currently popular solutions. The results of evaluation indicate a significant gain in both accuracy of predictions and reduction of the amount of test traffic which needs to be generated for measurements.
Published: 2022
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27. Wireless Local Area Network Technologies as Communication Solutions for Unmanned Surface Vehicles.

Author: Stateczny A, Gierlowski K, and Hoeft M
Abstract: As the number of research activities and practical deployments of unmanned vehicles has shown a rapid growth, topics related to their communication with operator and external infrastructure became of high importance. As a result a trend of employing IP communication for this purpose is emerging and can be expected to bring significant advantages. However, its employment can be expected to be most effective using broadband communication technologies such as Wireless Local Area Networks (WLANs). To verify the effectiveness of such an approach in a specific case of surface unmanned vehicles, the paper includes an overview of IP-based MAVLink communication advantages and requirements, followed by a laboratory and field-experiment study of selected WLAN technologies, compared to popular narrowband communication solutions. The conclusions confirm the general applicability of IP/WLAN communication for surface unmanned vehicles, providing an overview of their advantages and pointing out deployment requirements.
Published: 2022
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28. Needle-like structures discovered on positively charged lightning branches.

Author: Hare BM, Scholten O, Dwyer J, Trinh TNG, Buitink S, Ter Veen S, Bonardi A, Corstanje A, Falcke H, Hörandel JR, Huege T, Mitra P, Mulrey K, Nelles A, Rachen JP, Rossetto L, Schellart P, Winchen T, Anderson J, Avruch IM, Bentum MJ, Blaauw R, Broderick JW, Brouw WN, Brüggen M, Butcher HR, Ciardi B, Fallows RA, de Geus E, Duscha S, Eislöffel J, Garrett MA, Grießmeier JM, Gunst AW, van Haarlem MP, Hessels JWT, Hoeft M, van der Horst AJ, Iacobelli M, Koopmans LVE, Krankowski A, Maat P, Norden MJ, Paas H, Pandey-Pommier M, Pandey VN, Pekal R, Pizzo R, Reich W, Rothkaehl H, Röttgering HJA, Rowlinson A, Schwarz DJ, Shulevski A, Sluman J, Smirnov O, Soida M, Tagger M, Toribio MC, van Ardenne A, Wijers RAMJ, van Weeren RJ, Wucknitz O, Zarka P, and Zucca P
Abstract: Lightning is a dangerous yet poorly understood natural phenomenon. Lightning forms a network of plasma channels propagating away from the initiation point with both positively and negatively charged ends-called positive and negative leaders 1 . Negative leaders propagate in discrete steps, emitting copious radio pulses in the 30-300-megahertz frequency band 2-8 that can be remotely sensed and imaged with high spatial and temporal resolution 9-11 . Positive leaders propagate more continuously and thus emit very little high-frequency radiation 12 . Radio emission from positive leaders has nevertheless been mapped 13-15 , and exhibits a pattern that is different from that of negative leaders 11-13,16,17 . Furthermore, it has been inferred that positive leaders can become transiently disconnected from negative leaders 9,12,16,18-20 , which may lead to current pulses that both reconnect positive leaders to negative leaders 11,16,17,20-22 and cause multiple cloud-to-ground lightning events 1 . The disconnection process is thought to be due to negative differential resistance 18 , but this does not explain why the disconnections form primarily on positive leaders 22 , or why the current in cloud-to-ground lightning never goes to zero 23 . Indeed, it is still not understood how positive leaders emit radio-frequency radiation or why they behave differently from negative leaders. Here we report three-dimensional radio interferometric observations of lightning over the Netherlands with unprecedented spatiotemporal resolution. We find small plasma structures-which we call 'needles'-that are the dominant source of radio emission from the positive leaders. These structures appear to drain charge from the leader, and are probably the reason why positive leaders disconnect from negative ones, and why cloud-to-ground lightning connects to the ground multiple times.
Published: 2019
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29. Corrigendum: A large light-mass component of cosmic rays at 10 17 -10 17.5 electronvolts from radio observations.

Author: Buitink S, Corstanje A, Falcke H, Hörandel JR, Huege T, Nelles A, Rachen JP, Rossetto L, Schellart P, Scholten O, Ter Veen S, Thoudam S, Trinh TN, Anderson J, Asgekar A, Avruch IM, Bell ME, Bentum MJ, Bernardi G, Best P, Bonafede A, Breitling F, Broderick JW, Brouw WN, Brüggen M, Butcher HR, Carbone D, Ciardi B, Conway JE, de Gasperin F, de Geus E, Deller A, Dettmar RJ, van Diepen G, Duscha S, Eislöffel J, Engels D, Enriquez JE, Fallows RA, Fender R, Ferrari C, Frieswijk W, Garrett MA, Grießmeier JM, Gunst AW, van Haarlem MP, Hassall TE, Heald G, Hessels JW, Hoeft M, Horneffer A, Iacobelli M, Intema H, Juette E, Karastergiou A, Kondratiev VI, Kramer M, Kuniyoshi M, Kuper G, van Leeuwen J, Loose GM, Maat P, Mann G, Markoff S, McFadden R, McKay-Bukowski D, McKean JP, Mevius M, Mulcahy DD, Munk H, Norden MJ, Orru E, Paas H, Pandey-Pommier M, Pandey VN, Pietka M, Pizzo R, Polatidis AG, Reich W, Röttgering HJ, Scaife AM, Schwarz DJ, Serylak M, Sluman J, Smirnov O, Stappers BW, Steinmetz M, Stewart A, Swinbank J, Tagger M, Tang Y, Tasse C, Toribio MC, Vermeulen R, Vocks C, Vogt C, van Weeren RJ, Wijers RA, Wijnholds SJ, Wise MW, Wucknitz O, Yatawatta S, Zarka P, and Zensus JA
Published: 2016
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30. A large light-mass component of cosmic rays at 10(17)-10(17.5) electronvolts from radio observations.

Author: Buitink S, Corstanje A, Falcke H, Hörandel JR, Huege T, Nelles A, Rachen JP, Rossetto L, Schellart P, Scholten O, ter Veen S, Thoudam S, Trinh TN, Anderson J, Asgekar A, Avruch IM, Bell ME, Bentum MJ, Bernardi G, Best P, Bonafede A, Breitling F, Broderick JW, Brouw WN, Brüggen M, Butcher HR, Carbone D, Ciardi B, Conway JE, de Gasperin F, de Geus E, Deller A, Dettmar RJ, van Diepen G, Duscha S, Eislöffel J, Engels D, Enriquez JE, Fallows RA, Fender R, Ferrari C, Frieswijk W, Garrett MA, Grießmeier JM, Gunst AW, van Haarlem MP, Hassall TE, Heald G, Hessels JW, Hoeft M, Horneffer A, Iacobelli M, Intema H, Juette E, Karastergiou A, Kondratiev VI, Kramer M, Kuniyoshi M, Kuper G, van Leeuwen J, Loose GM, Maat P, Mann G, Markoff S, McFadden R, McKay-Bukowski D, McKean JP, Mevius M, Mulcahy DD, Munk H, Norden MJ, Orru E, Paas H, Pandey-Pommier M, Pandey VN, Pietka M, Pizzo R, Polatidis AG, Reich W, Röttgering HJ, Scaife AM, Schwarz DJ, Serylak M, Sluman J, Smirnov O, Stappers BW, Steinmetz M, Stewart A, Swinbank J, Tagger M, Tang Y, Tasse C, Toribio MC, Vermeulen R, Vocks C, Vogt C, van Weeren RJ, Wijers RA, Wijnholds SJ, Wise MW, Wucknitz O, Yatawatta S, Zarka P, and Zensus JA
Abstract: Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 10(17)-10(18) electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal comes from accelerators capable of producing cosmic rays of these energies. 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 maximum (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground. Current measurements have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays is a rapidly developing technique 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 front. 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 10(17)-10(17.5) 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 10(17.5) electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 10(17)-10(17.5) electronvolt range.
Published: 2016
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31. Particle acceleration on megaparsec scales in a merging galaxy cluster.

Author: van Weeren RJ, Röttgering HJ, Brüggen M, and Hoeft M
Abstract: Galaxy clusters form through a sequence of mergers of smaller galaxy clusters and groups. Models of diffusive shock acceleration suggest that in shocks that occur during cluster mergers, particles are accelerated to relativistic energies, similar to conditions within supernova remnants. In the presence of magnetic fields, these particles emit synchrotron radiation and may form so-called radio relics. We detected a radio relic that displays highly aligned magnetic fields, a strong spectral index gradient, and a narrow relic width, giving a measure of the magnetic field in an unexplored site of the universe. Our observations show that diffusive shock acceleration also operates on scales much larger than in supernova remnants and that shocks in galaxy clusters are capable of producing extremely energetic cosmic rays.
Published: 2010
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32. Mesenchymal stem cells regulate angiogenesis according to their mechanical environment.

Author: Kasper G, Dankert N, Tuischer J, Hoeft M, Gaber T, Glaeser JD, Zander D, Tschirschmann M, Thompson M, Matziolis G, and Duda GN
Subjects: Arthroplasty, Replacement, Hip, Bioreactors, Bone Marrow Cells cytology, Bone Marrow Cells physiology, Cell Division, Culture Media, Flow Cytometry, Humans, Receptors, Fibroblast Growth Factor physiology, Receptors, Vascular Endothelial Growth Factor physiology, Regeneration, Signal Transduction physiology, Mesenchymal Stem Cells cytology, Mesenchymal Stem Cells physiology, Neovascularization, Physiologic physiology
Abstract: In fracture and bone defect healing, MSCs largely drive tissue regeneration. MSCs have been shown to promote angiogenesis both in vivo and in vitro. Angiogenesis is a prerequisite to large tissue reconstitution. The present study investigated how mechanical loading of MSCs influences their proangiogenic capacity. The results show a significant enhancement of angiogenesis by conditioned media from mechanically stimulated compared with unstimulated MSCs in two-dimensional tube formation and three-dimensional spheroid sprouting assays. In particular, proliferation but not migration or adhesion of endothelial cells was elevated. Promotion of angiogenesis was dependent upon fibroblast growth factor receptor 1 (FGFR1) signaling. Moreover, stimulation of tube formation was inhibited by vascular endothelial growth factor receptor (VEGFR) tyrosine kinase blocking. Screening for the expression levels of different soluble regulators of angiogenesis revealed an enrichment of matrix metalloprotease 2, transforming growth factor beta1, and basic fibroblast growth factor but not of vascular endothelial growth factor in response to mechanical stimulation. In conclusion, mechanical loading of MSCs seems to result in a paracrine stimulation of angiogenesis, most likely by the regulation of a network of several angiogenic molecules. The underlying mechanism appears to be dependent on the FGFR and VEGFR signaling cascades and might be mediated by an additional cross-talk with other pathways.
Published: 2007
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32 results on '"M. Hoeft"'

1. Diffuse radio emission from non- Planck galaxy clusters in the LoTSS-DR2 fields

2. Radio fossils, relics, and haloes in Abell 3266: cluster archaeology with ASKAP-EMU and the ATCA

3. Deep low-frequency radio observations of Abell 2256

4. Deep low-frequency radio observations of Abell 2256 I: The filamentary radio relic

5. A 3.5 Mpc long radio relic in the galaxy cluster ClG 0217+70

6. The galaxy population within the virial radius of the Perseus cluster

7. Cassiopeia A, Cygnus A, Taurus A, and Virgo A at ultra-low radio frequencies

8. A galaxy cluster in the innermost Zone of Avoidance, close to the radio phoenix VLSS J2217.5+5943

9. The 'Sausage' and 'Toothbrush' clusters of galaxies and the prospects of LOFAR observations of clusters of galaxies

10. Corrigendum: A large light-mass component of cosmic rays at 10

11. Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes (Corrigendum)

12. LOFAR sparse image reconstruction

13. The LOFAR Multifrequency Snapshot Sky Survey (MSSS): I. Survey description and first results

14. Feedback in Active Galactic Nucleus Heating of Galaxy Clusters

15. The Scale‐dependent Energy Transfer Rate as a Tracer for Star Formation in CosmologicalN‐Body Simulations

16. Enhancement of the electron screening effect for d + d fusion reactions in metallic environments

17. LOFAR: The LOw-Frequency ARray

18. First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256

19. Wide-field LOFAR imaging of the field around the double-double radio galaxy B1834+620

20. Training a team with simulated team members

21. Simulations of magnetic fields in the cosmos.

22. Deep Very Large Array Observations of the Merging Cluster CIZA J2242.8+5301: Continuum and Spectral Imaging.

23. Deep VLA Observations of the Cluster 1RXS J0603.3+4214 in the Frequency Range of 1–2 GHz.

24. Merging the Worlds of Pets and Pills: Development and Evaluation of an Interprofessional Activity Linking Pharmacy and Veterinary Medicine.

25. Validation of Bayesian design for broadband microslit panel absorbers using causal inference.

26. Wireless Link Selection Methods for Maritime Communication Access Networks-A Deep Learning Approach.

27. Wireless Local Area Network Technologies as Communication Solutions for Unmanned Surface Vehicles.

28. Needle-like structures discovered on positively charged lightning branches.

29. Corrigendum: A large light-mass component of cosmic rays at 10 17 -10 17.5 electronvolts from radio observations.

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

31. Particle acceleration on megaparsec scales in a merging galaxy cluster.

32. Mesenchymal stem cells regulate angiogenesis according to their mechanical environment.

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32 results on '"M. Hoeft"'

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