Skip to main content

Research Repository

Advanced Search

A physical model for the spectral-timing properties of accreting black holes

Mahmoud, Ra’ad D; Done, Chris

A physical model for the spectral-timing properties of accreting black holes Thumbnail


Authors

Ra’ad D Mahmoud



Abstract

We develop new techniques to deconvolve the radial structure of the X-ray emission region in the bright low/hard state of the black hole Cygnus X-1 using both spectral and timing data in the 3–35 keV range. The spectrum at these energies is dominated by Comptonization rather than the disc, but there is a complex pattern in the time lags between different energy bands and differences in the normalization and shape in the power spectra of these bands, which clearly shows that the Comptonization is not produced from a single, homogeneous region. We use a physically based model of density fluctuations propagating through a spectrally inhomogeneous flow, setting the spectral components by jointly fitting to the time-averaged and Fourier-resolved spectra. The predicted variability in any band is modelled analytically in Fourier space so it can be fit directly to the observed power spectra and lags. We find that the best-fitting model picks out three distinct radii in the flow, each with a distinct Compton spectrum. The variability and luminosity produced at these radii is enhanced, while propagation of fluctuations from larger radii is suppressed. We associate these radii with the disc truncation, the inner edge of the flow, and (more speculatively) the jet launch radius. These distinct radii are most evident where the source is close to a transition between the low/hard and high/soft states. We suggest that the smoother power spectra seen at lower luminosities imply that the source structure is simpler away from the transition.

Citation

Mahmoud, R. D., & Done, C. (2018). A physical model for the spectral-timing properties of accreting black holes. Monthly Notices of the Royal Astronomical Society, 480(3), 4040-4059. https://doi.org/10.1093/mnras/sty2133

Journal Article Type Article
Acceptance Date Aug 3, 2018
Online Publication Date Aug 6, 2018
Publication Date Aug 6, 2018
Deposit Date Oct 31, 2018
Publicly Available Date Oct 31, 2018
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 480
Issue 3
Pages 4040-4059
DOI https://doi.org/10.1093/mnras/sty2133

Files

Published Journal Article (4.4 Mb)
PDF

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.







You might also like



Downloadable Citations