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

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-fi...

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Main Authors:	McKean, J., Godfrey, L., Vegetti, S., Wise, M., Morganti, R., Hardcastle, M., Rafferty, D., Anderson, J., Avruch, I., Beck, R., Bell, M., van Bemmel, I., Bentum, M., Bernardi, G., Best, P., Blaauw, R., Bonafede, A., Breitling, F., Broderick, J., Brueggen, M., Cerrigone, L., Ciardi, B., de Gasperin, F., Deller, A., Duscha, S., Engels, D., Falcke, H., Fallows, R., Frieswijk, W., Garrett, M., Griessmeier, J., van Haarlem, M., Heald, G., Hoeft, M., van der Horst, A., Iacobelli, M., Intema, Hubertus, Juette, E., Karastergiou, A., Kondratiev, V., Koopmans, L., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Mulcahy, D., Munk, H., Nelles, A., Orru, E., Paas, H., Pandey-Pommier, M., Pietka, M., Pizzo, R., Polatidis, A., Reich, W., Rottgering, H., Rowlinson, A., Scaife, A., Serylak, M., Shulevski, A., Sluman, J., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Thoudam, S., Toribio, M., Vermeulen, R., Vocks, C., van Weeren, R., Wucknitz, O., Yatawatta, S., Zarka, P.
Format:	Journal Article
Published:	Oxford University Press 2016
Online Access:	http://hdl.handle.net/20.500.11937/74248

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author	McKean, J. Godfrey, L. Vegetti, S. Wise, M. Morganti, R. Hardcastle, M. Rafferty, D. Anderson, J. Avruch, I. Beck, R. Bell, M. van Bemmel, I. Bentum, M. Bernardi, G. Best, P. Blaauw, R. Bonafede, A. Breitling, F. Broderick, J. Brueggen, M. Cerrigone, L. Ciardi, B. de Gasperin, F. Deller, A. Duscha, S. Engels, D. Falcke, H. Fallows, R. Frieswijk, W. Garrett, M. Griessmeier, J. van Haarlem, M. Heald, G. Hoeft, M. van der Horst, A. Iacobelli, M. Intema, Hubertus Juette, E. Karastergiou, A. Kondratiev, V. Koopmans, L. Kuniyoshi, M. Kuper, G. van Leeuwen, J. Maat, P. Mann, G. Markoff, S. McFadden, R. McKay-Bukowski, D. Mulcahy, D. Munk, H. Nelles, A. Orru, E. Paas, H. Pandey-Pommier, M. Pietka, M. Pizzo, R. Polatidis, A. Reich, W. Rottgering, H. Rowlinson, A. Scaife, A. Serylak, M. Shulevski, A. Sluman, J. Smirnov, O. Steinmetz, M. Stewart, A. Swinbank, J. Tagger, M. Thoudam, S. Toribio, M. Vermeulen, R. Vocks, C. van Weeren, R. Wucknitz, O. Yatawatta, S. Zarka, P.
author_facet	McKean, J. Godfrey, L. Vegetti, S. Wise, M. Morganti, R. Hardcastle, M. Rafferty, D. Anderson, J. Avruch, I. Beck, R. Bell, M. van Bemmel, I. Bentum, M. Bernardi, G. Best, P. Blaauw, R. Bonafede, A. Breitling, F. Broderick, J. Brueggen, M. Cerrigone, L. Ciardi, B. de Gasperin, F. Deller, A. Duscha, S. Engels, D. Falcke, H. Fallows, R. Frieswijk, W. Garrett, M. Griessmeier, J. van Haarlem, M. Heald, G. Hoeft, M. van der Horst, A. Iacobelli, M. Intema, Hubertus Juette, E. Karastergiou, A. Kondratiev, V. Koopmans, L. Kuniyoshi, M. Kuper, G. van Leeuwen, J. Maat, P. Mann, G. Markoff, S. McFadden, R. McKay-Bukowski, D. Mulcahy, D. Munk, H. Nelles, A. Orru, E. Paas, H. Pandey-Pommier, M. Pietka, M. Pizzo, R. Polatidis, A. Reich, W. Rottgering, H. Rowlinson, A. Scaife, A. Serylak, M. Shulevski, A. Sluman, J. Smirnov, O. Steinmetz, M. Stewart, A. Swinbank, J. Tagger, M. Thoudam, S. Toribio, M. Vermeulen, R. Vocks, C. van Weeren, R. Wucknitz, O. Yatawatta, S. Zarka, P.
author_sort	McKean, J.
building	Curtin Institutional Repository
collection	Online Access
description	The low-frequency radio spectra of the hotspots within powerful radio galaxies can provide valuable information about the physical processes operating at the site of the jet termination. These processes are responsible for the dissipation of jet kinetic energy, particle acceleration, and magnetic-field generation. Here, we report new observations of the powerful radio galaxy Cygnus A using the Low Frequency Array (LOFAR) between 109 and 183 MHz, at an angular resolution of ∼3.5 arcsec. The radio emission of the lobes is found to have a complex spectral index distribution, with a spectral steepening found towards the centre of the source. For the first time, a turnover in the radio spectrum of the two main hotspots of Cygnus A has been directly observed. By combining our LOFAR imaging with data from the Very Large Array at higher frequencies, we show that the very rapid turnover in the hotspot spectra cannot be explained by a low-energy cut-off in the electron energy distribution, as has been previously suggested. Thermal (free–free) absorption or synchrotron self-absorption models are able to describe the low-frequency spectral shape of the hotspots; however, as with previous studies, we find that the implied model parameters are unlikely, and interpreting the spectra of the hotspots remains problematic.
first_indexed	2025-11-14T11:00:00Z
format	Journal Article
id	curtin-20.500.11937-74248
institution	Curtin University Malaysia
institution_category	Local University
last_indexed	2025-11-14T11:00:00Z
publishDate	2016
publisher	Oxford University Press
recordtype	eprints
repository_type	Digital Repository
spelling	curtin-20.500.11937-742482019-03-13T00:53:37Z LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra McKean, J. Godfrey, L. Vegetti, S. Wise, M. Morganti, R. Hardcastle, M. Rafferty, D. Anderson, J. Avruch, I. Beck, R. Bell, M. van Bemmel, I. Bentum, M. Bernardi, G. Best, P. Blaauw, R. Bonafede, A. Breitling, F. Broderick, J. Brueggen, M. Cerrigone, L. Ciardi, B. de Gasperin, F. Deller, A. Duscha, S. Engels, D. Falcke, H. Fallows, R. Frieswijk, W. Garrett, M. Griessmeier, J. van Haarlem, M. Heald, G. Hoeft, M. van der Horst, A. Iacobelli, M. Intema, Hubertus Juette, E. Karastergiou, A. Kondratiev, V. Koopmans, L. Kuniyoshi, M. Kuper, G. van Leeuwen, J. Maat, P. Mann, G. Markoff, S. McFadden, R. McKay-Bukowski, D. Mulcahy, D. Munk, H. Nelles, A. Orru, E. Paas, H. Pandey-Pommier, M. Pietka, M. Pizzo, R. Polatidis, A. Reich, W. Rottgering, H. Rowlinson, A. Scaife, A. Serylak, M. Shulevski, A. Sluman, J. Smirnov, O. Steinmetz, M. Stewart, A. Swinbank, J. Tagger, M. Thoudam, S. Toribio, M. Vermeulen, R. Vocks, C. van Weeren, R. Wucknitz, O. Yatawatta, S. Zarka, P. The low-frequency radio spectra of the hotspots within powerful radio galaxies can provide valuable information about the physical processes operating at the site of the jet termination. These processes are responsible for the dissipation of jet kinetic energy, particle acceleration, and magnetic-field generation. Here, we report new observations of the powerful radio galaxy Cygnus A using the Low Frequency Array (LOFAR) between 109 and 183 MHz, at an angular resolution of ∼3.5 arcsec. The radio emission of the lobes is found to have a complex spectral index distribution, with a spectral steepening found towards the centre of the source. For the first time, a turnover in the radio spectrum of the two main hotspots of Cygnus A has been directly observed. By combining our LOFAR imaging with data from the Very Large Array at higher frequencies, we show that the very rapid turnover in the hotspot spectra cannot be explained by a low-energy cut-off in the electron energy distribution, as has been previously suggested. Thermal (free–free) absorption or synchrotron self-absorption models are able to describe the low-frequency spectral shape of the hotspots; however, as with previous studies, we find that the implied model parameters are unlikely, and interpreting the spectra of the hotspots remains problematic. 2016 Journal Article http://hdl.handle.net/20.500.11937/74248 10.1093/mnras/stw2105 Oxford University Press fulltext
spellingShingle	McKean, J. Godfrey, L. Vegetti, S. Wise, M. Morganti, R. Hardcastle, M. Rafferty, D. Anderson, J. Avruch, I. Beck, R. Bell, M. van Bemmel, I. Bentum, M. Bernardi, G. Best, P. Blaauw, R. Bonafede, A. Breitling, F. Broderick, J. Brueggen, M. Cerrigone, L. Ciardi, B. de Gasperin, F. Deller, A. Duscha, S. Engels, D. Falcke, H. Fallows, R. Frieswijk, W. Garrett, M. Griessmeier, J. van Haarlem, M. Heald, G. Hoeft, M. van der Horst, A. Iacobelli, M. Intema, Hubertus Juette, E. Karastergiou, A. Kondratiev, V. Koopmans, L. Kuniyoshi, M. Kuper, G. van Leeuwen, J. Maat, P. Mann, G. Markoff, S. McFadden, R. McKay-Bukowski, D. Mulcahy, D. Munk, H. Nelles, A. Orru, E. Paas, H. Pandey-Pommier, M. Pietka, M. Pizzo, R. Polatidis, A. Reich, W. Rottgering, H. Rowlinson, A. Scaife, A. Serylak, M. Shulevski, A. Sluman, J. Smirnov, O. Steinmetz, M. Stewart, A. Swinbank, J. Tagger, M. Thoudam, S. Toribio, M. Vermeulen, R. Vocks, C. van Weeren, R. Wucknitz, O. Yatawatta, S. Zarka, P. LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra
title	LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra
title_full	LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra
title_fullStr	LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra
title_full_unstemmed	LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra
title_short	LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra
title_sort	lofar imaging of cygnus a - direct detection of a turnover in the hotspot radio spectra
url	http://hdl.handle.net/20.500.11937/74248

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

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