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

Mckean JP, Godfrey LEH, Vegetti S, Wise MW, Morganti R, Hardcastle MJ, Rafferty D, Anderson J, Avruch IM, Beck R, Bell ME, Van Bemmel I, Bentum MJ, Bernardi G, Best P, Blaauw R, Bonafede A, Breitling F, Broderick JW, Brueggen M, Cerrigone L, Ciardi B, De Gasperin F, Deller A, Duscha S, Engels D, Falcke H, Fallows RA, Frieswijk W, Garrett MA, Griessmeier JM, Van Haarlem MP, Heald G, Hoeft M, Van Der Horst AJ, Iacobelli M, Intema H, Juette E, Karastergiou A, Kondratiev VI, Koopmans LVE, Kuniyoshi M, Kuper G, Van Leeuwen J, Maat P, Mann G, Markoff S, Mcfadden R, Mckay-Bukowski D, Mulcahy DD, Munk H, Nelles A, Orru E, Paas H, Pandey-Pommier M, Pietka M, Pizzo R, Polatidis AG, Reich W, Rottgering HJA, Rowlinson A, Scaife AMM, Serylak M, Shulevski A, Sluman J, Smirnov O, Steinmetz M, Stewart A, Swinbank J, Tagger M, Thoudam S, Toribio MC, Vermeulen R, Vocks C, Van Weeren RJ, Wucknitz O, Yatawatta S, Zarka P (2016)

Publication Status: Published

Publication Type: Journal article

Publication year: 2016

Journal

Publisher: OXFORD UNIV PRESS

Book Volume: 463

Pages Range: 3143-3150

Journal Issue: 3

DOI: 10.1093/mnras/stw2105

Abstract

The low-frequency radio spectra of the hotspots within powerful radio galaxies can provide valuable information about the physical processes operating at the site of the jet termination. These processes are responsible for the dissipation of jet kinetic energy, particle acceleration, and magnetic-field generation. Here, we report new observations of the powerful radio galaxy Cygnus A using the Low Frequency Array (LOFAR) between 109 and 183 MHz, at an angular resolution of similar to 3.5 arcsec. The radio emission of the lobes is found to have a complex spectral index distribution, with a spectral steepening found towards the centre of the source. For the first time, a turnover in the radio spectrum of the two main hotspots of Cygnus A has been directly observed. By combining our LOFAR imaging with data from the Very Large Array at higher frequencies, we show that the very rapid turnover in the hotspot spectra cannot be explained by a low-energy cut-off in the electron energy distribution, as has been previously suggested. Thermal (free-free) absorption or synchrotron self-absorption models are able to describe the low-frequency spectral shape of the hotspots; however, as with previous studies, we find that the implied model parameters are unlikely, and interpreting the spectra of the hotspots remains problematic.

Authors with CRIS profile

Involved external institutions

Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. (MPG) / Max Planck Society for the Advancement of Science Germany (DE) University of California Irvine United States (USA) (US) Netherlands Institute for Radio Astronomy Netherlands (NL) University of Groningen / Rijksuniversiteit Groningen Netherlands (NL) Ruhr-Universität Bochum (RUB) Germany (DE) National Astronomical Observatory of Japan / 国立天文台(NAOJ) Japan (JP) University of Orléans / Université d'Orléans France (FR) University of Oxford United Kingdom (GB) Max-Planck-Institut für Radioastronomie / Max Planck Institute for Radio Astronomy Germany (DE) SKA South Africa South Africa (ZA) Leibniz Institute for Astrophysics Potsdam / Leibniz-Institut für Astrophysik Potsdam Germany (DE) Harvard University United States (USA) (US) University of Manchester United Kingdom (GB) University of the Western Cape (UWC) South Africa (ZA) PSL Research University / Université de recherche Paris Sciences et Lettres France (FR) Joint Institute for VLBI in Europe (JIVE) Netherlands (NL) Princeton University United States (USA) (US) University of Edinburgh United Kingdom (GB) University of Hertfordshire United Kingdom (GB) University of Amsterdam Netherlands (NL) Oulun Yliopisto / University of Oulo Finland (FI) Leiden University Netherlands (NL) Observatoire de Lyon France (FR) University of Southampton United Kingdom (GB) Thüringer Landessternwarte Tautenburg (TLS) - Karl-Schwarzschild-Observatorium Germany (DE) Universität Hamburg (UHH) Germany (DE) Australia Telescope National Facility (ATNF) Australia (AU) George Washington University (GWU) United States (USA) (US) Radboud University Nijmegen Netherlands (NL) Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ Germany (DE)

How to cite

APA:

Mckean, J.P., Godfrey, L.E.H., Vegetti, S., Wise, M.W., Morganti, R., Hardcastle, M.J.,... Zarka, P. (2016). LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra. Monthly Notices of the Royal Astronomical Society, 463(3), 3143-3150. https://doi.org/10.1093/mnras/stw2105

MLA:

Mckean, J. P., et al. "LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra." Monthly Notices of the Royal Astronomical Society 463.3 (2016): 3143-3150.

BibTeX: Download