Journal Article

The ubiquity of the rms–flux relation in black hole X-ray binaries

L. M. Heil, S. Vaughan and P. Uttley

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 422, issue 3, pages 2620-2631
Published in print May 2012 | ISSN: 0035-8711
Published online May 2012 | e-ISSN: 1365-2966 | DOI:
The ubiquity of the rms–flux relation in black hole X-ray binaries

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We have investigated the short-term linear relation between the rms variability and the flux in 1961 observations of nine black hole X-ray binaries. The rms–flux relation for the 1–10 Hz range is ubiquitously observed in any observation with good variability signal-to-noise ratio (>3 per cent, 1–10 Hz fractional rms). This concurs with results from a previous study of Cygnus X-1, and extends detection of the rms–flux relation to a wider range of states. We find a strong dependence of the flux intercept of the rms–flux relation on source state; as the source transitions from the hard state into the hard intermediate state, the intercept becomes strongly positive. We find little evidence for flux dependence of the broad-band noise within the power spectra shape, excepting a small subset of observations from one object in an anomalous soft state. We speculate that the ubiquitous linear rms–flux relation in the broad-band noise of this sample, representing a range of different states and objects, indicates that its formation mechanism is an essential property of the luminous accretion flow around black holes.

Keywords: X-rays: binaries; X-rays: general

Journal Article.  7904 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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