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Chandra Observations of Cygnus A: Magnetic Field Strengths in the Hot Spots of a Radio Galaxy

Wilson, A. S. and Young, A. J. and Shopbell, P. L. (2000) Chandra Observations of Cygnus A: Magnetic Field Strengths in the Hot Spots of a Radio Galaxy. Astrophysical Journal, 544 (1). L27-L30. ISSN 0004-637X. doi:10.1086/317293.

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We report X-ray observations of the powerful radio galaxy Cygnus A with the Chandra X-Ray Observatory. This Letter focuses on the radio hot spots, all four of which are detected in X-rays with a very similar morphology to their radio structure. X-ray spectra have been obtained for the two brighter hot spots (A and D). Both are well described by a power law with photon index Γ = 1.8 ± 0.2 absorbed by the Galactic column in the direction of Cygnus A. Thermal X-ray models require too high gas densities and may be ruled out. The images and spectra strongly support synchrotron self-Compton models of the X-ray emission, as proposed by Harris, Carilli, & Perley on the basis of ROSAT imaging observations. Such models indicate that the magnetic field in each of the brighter hot spots is 1.5 × 10^(-4) G, with an uncertainty of a few tens of percent. This value is close to the equipartition field strengths assuming no protons are present. The possibility that the X-rays are synchrotron radiation is briefly discussed but not favored. We speculate that production of the γ ~ 107 electrons necessary for X-ray synchrotron radiation from hot spots is inhibited when the external gas density is high, as is the case when the radio galaxy is within a cooling flow.

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Additional Information:© 2000. The American Astronomical Society. Received 2000 July 28; accepted 2000 September 18; published 2000 November 8. We are grateful to Rick Perley for providing the VLA 6 cm map of Cygnus A in numerical form. We also wish to thank the staff of the Chandra Science Center, especially Dan Harris and Shanil Virani, for their help. This research was supported by NASA grant NAG-81027 and by the Graduate School of the University of Maryland.
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University of MarylandUNSPECIFIED
Subject Keywords:galaxies: active; galaxies: individual (Cygnus A) ; galaxies: jets; galaxies: nuclei; magnetic fields; X-rays: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20170408-135513444
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Official Citation:A. S. Wilson et al 2000 ApJ 544 L27
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75887
Deposited By: 1Science Import
Deposited On:13 Apr 2017 21:56
Last Modified:15 Nov 2021 16:55

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