Journal Article

Black hole accretion discs in the canonical low-hard state

R. C. Reis, A. C. Fabian and J. M. Miller

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 2, pages 836-854
Published in print February 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI:
Black hole accretion discs in the canonical low-hard state

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Stellar mass black holes in the low-hard state may hold clues to jet formation and basic accretion disc physics, but the nature of the accretion flow remains uncertain. A standard thin disc can extend close to the innermost stable circular orbit, but the inner disc may evaporate when the mass accretion rate is reduced. Blackbody-like continuum emission and dynamically broadened iron emission lines provide independent means of probing the radial extent of the inner disc. Here, we present an X-ray study of eight black holes in the low-hard state. A thermal-disc continuum with a colour temperature consistent with LT4 is clearly detected in all eight sources, down to ≈5 × 10−4LEdd. In six sources, disc models exclude a truncation radius larger than 10rg. Iron Kα fluorescence line emission is observed in half of the sample, down to luminosities of ≈1.5 × 10−3LEdd. Detailed fits to the line profiles exclude a truncated disc in each case. If strong evidence of truncation is defined as (1) a non-detection of a broad iron line and (2) an inner disc temperature much cooler than expected from the LT4 relation, none of the spectra in this sample offers strong evidence of disc truncation. This suggests that the inner disc may evaporate at or below ≈1.5 × 10−3LEdd.

Keywords: accretion, accretion discs

Journal Article.  13009 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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