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

J.~P. McKean; L.~E.~H. Godfrey; S. Vegetti; M.~W. Wise; R. Morganti; M.~J. Hardcastle; D. Rafferty; J. Anderson; I.~M. Avruch; R. Beck; M.~E. Bell; I. van Bemmel; M.~J. Bentum; G. Bernardi; P. Best; R. Blaauw; A. Bonafede; F. Breitling; J.~W. Broderick; M. Brüggen; L. Cerrigone; B. Ciardi; F. de Gasperin; A. Deller; S. Duscha; D. Engels; H. Falcke; R.~A. Fallows; W. Frieswijk; Michael Garrett; J.~M. Grießmeier; M.~P. van Haarlem; G. Heald; M. Hoeft; A.~J.~v.~d. Horst; M. Iacobelli; H. Intema; E. Juette; A. Karastergiou; V.~I. Kondratiev; L.~V.~E. Koopmans; M. Kuniyoshi; G. Kuper; J. van Leeuwen; P. Maat; G. Mann; S. Markoff; R. McFadden; D. McKay-Bukowski; D D Mulcahy; H. Munk; A. Nelles; E. Orru; H. Paas; M. Pandey-Pommier; M. Pietka; R. Pizzo; A.~G. Polatidis; W. Reich; H.~J.~A. Röttgering; A. Rowlinson; Anna Scaife; M. Serylak; A. Shulevski; J. Sluman; O. Smirnov; M. Steinmetz; A. Stewart; J. Swinbank; M. Tagger; S. Thoudam; M.~C. Toribio; R. Vermeulen; C. Vocks; R.~J. van Weeren; O. Wucknitz; S. Yatawatta; P. Zarka

doi:10.1093/mnras/stw2105

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

J.~P. McKean, L.~E.~H. Godfrey, S. Vegetti, M.~W. Wise, R. Morganti, M.~J. Hardcastle, D. Rafferty, J. Anderson, I.~M. Avruch, R. Beck, M.~E. Bell, I. van Bemmel, M.~J. Bentum, G. Bernardi, P. Best, R. Blaauw, A. Bonafede, F. Breitling, J.~W. Broderick, M. BrüggenL. Cerrigone, B. Ciardi, F. de Gasperin, A. Deller, S. Duscha, D. Engels, H. Falcke, R.~A. Fallows, W. Frieswijk, Michael Garrett, J.~M. Grießmeier, M.~P. van Haarlem, G. Heald, M. Hoeft, A.~J.~v.~d. Horst, M. Iacobelli, H. Intema, E. Juette, A. Karastergiou, V.~I. Kondratiev, L.~V.~E. Koopmans, M. Kuniyoshi, G. Kuper, J. van Leeuwen, P. Maat, G. Mann, S. Markoff, R. McFadden, D. McKay-Bukowski, D D Mulcahy, H. Munk, A. Nelles, E. Orru, H. Paas, M. Pandey-Pommier, M. Pietka, R. Pizzo, A.~G. Polatidis, W. Reich, H.~J.~A. Röttgering, A. Rowlinson, Anna Scaife, M. Serylak, A. Shulevski, J. Sluman, O. Smirnov, M. Steinmetz, A. Stewart, J. Swinbank, M. Tagger, S. Thoudam, M.~C. Toribio, R. Vermeulen, C. Vocks, R.~J. van Weeren, O. Wucknitz, S. Yatawatta, P. Zarka

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Abstract

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

Original language	Undefined
Pages (from-to)	3143-3150
Number of pages	8
Journal	MNRAS
Volume	463
Issue number	3
Early online date	24 Aug 2016
DOIs	https://doi.org/10.1093/mnras/stw2105
Publication status	Published - 11 Dec 2016

Keywords

radio continuum: galaxies

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10.1093/mnras/stw2105

stw2105Final published version, 680 KB

Cite this

McKean, J. P., Godfrey, L. E. H., Vegetti, S., Wise, M. W., Morganti, R., Hardcastle, M. J., Rafferty, D., Anderson, J., Avruch, I. M., Beck, R., Bell, M. E., van Bemmel, I., Bentum, M. J., Bernardi, G., Best, P., Blaauw, R., Bonafede, A., Breitling, F., Broderick, J. W., ... Zarka, P. (2016). LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra. MNRAS, 463(3), 3143-3150. https://doi.org/10.1093/mnras/stw2105

@article{88107cc7ee884cc9ba7e91bafe75ec69,

title = "LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra",

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

keywords = "radio continuum: galaxies",

author = "J.~P. McKean and L.~E.~H. Godfrey and S. Vegetti and M.~W. Wise and R. Morganti and M.~J. Hardcastle and D. Rafferty and J. Anderson and I.~M. Avruch and R. Beck and M.~E. Bell and {van Bemmel}, I. and M.~J. Bentum and G. Bernardi and P. Best and R. Blaauw and A. Bonafede and F. Breitling and J.~W. Broderick and M. Br{\"u}ggen and L. Cerrigone and B. Ciardi and {de Gasperin}, F. and A. Deller and S. Duscha and D. Engels and H. Falcke and R.~A. Fallows and W. Frieswijk and Michael Garrett and J.~M. Grie{\ss}meier and {van Haarlem}, M.~P. and G. Heald and M. Hoeft and A.~J.~v.~d. Horst and M. Iacobelli and H. Intema and E. Juette and A. Karastergiou and V.~I. Kondratiev and L.~V.~E. Koopmans and M. Kuniyoshi and G. Kuper and {van Leeuwen}, J. and P. Maat and G. Mann and S. Markoff and R. McFadden and D. McKay-Bukowski and Mulcahy, {D D} and H. Munk and A. Nelles and E. Orru and H. Paas and M. Pandey-Pommier and M. Pietka and R. Pizzo and A.~G. Polatidis and W. Reich and H.~J.~A. R{\"o}ttgering and A. Rowlinson and Anna Scaife and M. Serylak and A. Shulevski and J. Sluman and O. Smirnov and M. Steinmetz and A. Stewart and J. Swinbank and M. Tagger and S. Thoudam and M.~C. Toribio and R. Vermeulen and C. Vocks and {van Weeren}, R.~J. and O. Wucknitz and S. Yatawatta and P. Zarka",

year = "2016",

month = dec,

day = "11",

doi = "10.1093/mnras/stw2105",

language = "Undefined",

volume = "463",

pages = "3143--3150",

journal = "MNRAS",

issn = "1365-2966",

publisher = "Oxford University Press",

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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, Brüggen, M, Cerrigone, L, Ciardi, B, de Gasperin, F, Deller, A, Duscha, S, Engels, D, Falcke, H, Fallows, RA, Frieswijk, W, Garrett, M, Grießmeier, JM, van Haarlem, MP, Heald, G, Hoeft, M, 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, Röttgering, HJA, Rowlinson, A, Scaife, A, 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, 'LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra', MNRAS, vol. 463, no. 3, pp. 3143-3150. https://doi.org/10.1093/mnras/stw2105

TY - JOUR

T1 - LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra

AU - McKean, J.~P.

AU - Godfrey, L.~E.~H.

AU - Vegetti, S.

AU - Wise, M.~W.

AU - Morganti, R.

AU - Hardcastle, M.~J.

AU - Rafferty, D.

AU - Anderson, J.

AU - Avruch, I.~M.

AU - Beck, R.

AU - Bell, M.~E.

AU - van Bemmel, I.

AU - Bentum, M.~J.

AU - Bernardi, G.

AU - Best, P.

AU - Blaauw, R.

AU - Bonafede, A.

AU - Breitling, F.

AU - Broderick, J.~W.

AU - Brüggen, M.

AU - Cerrigone, L.

AU - Ciardi, B.

AU - de Gasperin, F.

AU - Deller, A.

AU - Duscha, S.

AU - Engels, D.

AU - Falcke, H.

AU - Fallows, R.~A.

AU - Frieswijk, W.

AU - Garrett, Michael

AU - Grießmeier, J.~M.

AU - van Haarlem, M.~P.

AU - Heald, G.

AU - Hoeft, M.

AU - Horst, A.~J.~v.~d.

AU - Iacobelli, M.

AU - Intema, H.

AU - Juette, E.

AU - Karastergiou, A.

AU - Kondratiev, V.~I.

AU - Koopmans, L.~V.~E.

AU - Kuniyoshi, M.

AU - Kuper, G.

AU - van Leeuwen, J.

AU - Maat, P.

AU - Mann, G.

AU - Markoff, S.

AU - McFadden, R.

AU - McKay-Bukowski, D.

AU - Mulcahy, D D

AU - Munk, H.

AU - Nelles, A.

AU - Orru, E.

AU - Paas, H.

AU - Pandey-Pommier, M.

AU - Pietka, M.

AU - Pizzo, R.

AU - Polatidis, A.~G.

AU - Reich, W.

AU - Röttgering, H.~J.~A.

AU - Rowlinson, A.

AU - Scaife, Anna

AU - Serylak, M.

AU - Shulevski, A.

AU - Sluman, J.

AU - Smirnov, O.

AU - Steinmetz, M.

AU - Stewart, A.

AU - Swinbank, J.

AU - Tagger, M.

AU - Thoudam, S.

AU - Toribio, M.~C.

AU - Vermeulen, R.

AU - Vocks, C.

AU - van Weeren, R.~J.

AU - Wucknitz, O.

AU - Yatawatta, S.

AU - Zarka, P.

PY - 2016/12/11

Y1 - 2016/12/11

N2 - 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.

AB - 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.

KW - radio continuum: galaxies

U2 - 10.1093/mnras/stw2105

DO - 10.1093/mnras/stw2105

M3 - Article

SN - 1365-2966

VL - 463

SP - 3143

EP - 3150

JO - MNRAS

JF - MNRAS

IS - 3

ER -