The similarity of broad iron lines in X-ray binaries and active galactic nuclei

Authors

D. J. Walton, Institute of Astronomy, University of Cambridge
R. C. Reis, Institute of Astronomy, University of Cambridge
E. M. Cackett, Institute of Astronomy, University of CambridgeFollow
A. C. Fabian, Institute of Astronomy, University of Cambridge
J. M. Miller, University of Michigan

Document Type

Article

Abstract

We have compared the 2001 XMM-Newton spectra of the stellar mass black hole binary XTE J1650-500 and the active galaxy MCG-6-30-15, focusing on the broad, excess emission features at ˜4-7 keV displayed by both sources. Such features are frequently observed in both low-mass X-ray binaries and active galactic nuclei (AGN). For the former case it is generally accepted that the excess arises due to iron emission, but there is some controversy over whether their width is partially enhanced by instrumental processes, and hence also over the intrinsic broadening mechanism. Meanwhile, in the latter case, the origin of this feature is still subject to debate; physically motivated reflection and absorption interpretations are both able to reproduce the observed spectra. In this work we make use of the contemporaneous BeppoSAX data to demonstrate that the breadth of the excess observed in XTE J1650-500 is astrophysical rather than instrumental, and proceed to highlight the similarity of the excesses present in this source and MCG-6-30-15. Both optically thick accretion discs and optically thin coronae, which in combination naturally give rise to relativistically broadened iron lines when the disc extends close to the black hole, are commonly observed in both classes of object. The simplest solution is that the broad emission features present arise from a common process, which we argue must be reflection from the inner regions of an accretion disc around a rapidly rotating black hole; for XTE J1650-500 we find spin constraints of 0.84 ≤a*≤ 0.98 at the 90 per cent confidence level. Other interpretations proposed for AGN add potentially unnecessary complexities to the theoretical framework of accretion in strong gravity.

Disciplines

External Galaxies | Stars, Interstellar Medium and the Galaxy

Comments

NOTICE IN COMPLIANCE WITH PUBLISHER POLICY: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©2012 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved. Available at doi:10.1111/j.1365-2966.2012.20809.x

Recommended Citation

Walton, D. J., Reis, R. C., Cackett, E. M., Fabian, A. C., Miller, J. M. 2012. The similarity of broad iron lines in X-ray binaries and active galactic nuclei. MNRAS 422(3), 2510-2531.