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Breaking the spectral degeneracies in black hole binaries with fast timing data: the hard state of Cygnus X-1

Axelsson, Magnus; Done, Chris

Breaking the spectral degeneracies in black hole binaries with fast timing data: the hard state of Cygnus X-1 Thumbnail


Authors

Magnus Axelsson



Abstract

The spectra of black hole binaries in the low/hard state are complex, with evidence for multiple different Comptonization regions contributing to the hard X-rays in addition to a cool disc component. We show this explicitly for some of the best RXTE data from Cyg X-1, where the spectrum strongly requires (at least) two different Comptonization components in order to fit the continuum above 3 keV, where the disc does not contribute. However, it is difficult to constrain the physical properties of these Comptonization components uniquely using spectral data alone. Instead, we show that additional information from fast variability can break this degeneracy. Specifically, we use the observed variability power spectra in each energy channel to reconstruct the energy spectra of the variability on time-scales of ∼10, 1, and 0.1 s. The two longer time-scale spectra have similar shapes, but the fastest component is dramatically harder, and has strong curvature indicating that its seed photons are not from the cool disc. We interpret this in the context of propagating fluctuations through a hot flow, where the outer regions are cooler and optically thick, so that they shield the inner region from the disc. The seed photons for the hot inner region are then from the cooler Comptonization region rather than the disc itself.

Citation

Axelsson, M., & Done, C. (2018). Breaking the spectral degeneracies in black hole binaries with fast timing data: the hard state of Cygnus X-1. Monthly Notices of the Royal Astronomical Society, 480(1), 751-758. https://doi.org/10.1093/mnras/sty1801

Journal Article Type Article
Acceptance Date Jul 3, 2018
Online Publication Date Jul 7, 2018
Publication Date Oct 11, 2018
Deposit Date Jul 4, 2018
Publicly Available Date Jul 4, 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 1
Pages 751-758
DOI https://doi.org/10.1093/mnras/sty1801

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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.






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