Journal Article

Radio and X-ray emission from disc winds in radio-quiet quasars

K. C. Steenbrugge, E. J. D. Jolley, Z. Kuncic and K. M. Blundell

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 413, issue 3, pages 1735-1743
Published in print May 2011 | ISSN: 0035-8711
Published online May 2011 | e-ISSN: 1365-2966 | DOI:
Radio and X-ray emission from disc winds in radio-quiet quasars

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It has been proposed that the radio spectra of radio-quiet quasars are produced by free–free emission in the optically thin part of an accretion disc wind. An important observational constraint on this model is the observed X-ray luminosity. We investigate this constraint using a sample of Palomar–Green (PG) radio-quiet quasars for which XMM–Newton European Photon Imaging Camera (EPIC) spectra are available. Comparing the predicted and measured luminosities for 0.5, 2 and 5 keV, we conclude that all of the studied PG quasars require a large hydrogen column density absorber, requiring these quasars to be close to or Compton thick. Such a large column density can be directly excluded for PG 0050+124, for which a high-resolution reflection grating spectrometer spectrum exists. Further constraint on the column density for a further 19 out of the 21 studied PG quasars comes from the EPIC spectrum characteristics such as hard X-ray power-law photon index and the equivalent width of the Fe Kα line; and the small equivalent width of the C iv absorber present in ultraviolet spectra. For two sources, PG 1001+054 and PG 1411+442, we cannot exclude that they are indeed Compton thick, and the radio and X-ray luminosity are due to a wind originating close to the supermassive black hole. We conclude that for 20 out of 22 PG quasars studied, free–free emission from a wind emanating from the accretion disc cannot mutually explain the observed radio and X-ray luminosity.

Keywords: plasmas; quasars: general; radio continuum: galaxies; X-rays: galaxies

Journal Article.  8145 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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