Skip to main content

Research Repository

Advanced Search

An imperfect double: probing the physical origin of the low-frequency quasi-periodic oscillation and its harmonic in black hole binaries

Axelsson, M.; Done, C.; Hjalmarsdotter, L.

An imperfect double: probing the physical origin of the low-frequency quasi-periodic oscillation and its harmonic in black hole binaries Thumbnail


Authors

M. Axelsson

L. Hjalmarsdotter



Abstract

We extract the spectra of the strong low-frequency quasi-periodic oscillation (QPO) and its harmonic during the rising phase of an outburst in the black hole binary XTE J1550-564. We compare these frequency-resolved spectra to the time-averaged spectrum and the spectrum of the rapid (<0.1 s) variability. The spectrum of the time-averaged emission can be described by a disc, a Compton upscattered tail and its reflection. The QPO spectrum is very similar to the spectrum of the most rapid variability, implying it arises in the innermost regions of the flow. It contains little detectable disc, and its Compton spectrum is generally harder and shows less reflection than in the time-averaged emission. The harmonic likewise contains little detectable disc component, but has a Compton spectrum which is systematically softer than the QPO, softer even than the Compton tail in the time-averaged emission. We interpret these results in the context of the truncated disc model, where the inner disc is replaced by a hot flow. The QPO can arise in this picture from vertical (Lense–Thirring) precession of the entire hot inner flow, and its harmonic can be produced by the angular dependence of Compton scattering within the hot flow. We extend these models to include stratification of the hot flow, so that it is softer (lower optical depth) at larger radii closer to the truncated disc, and harder (higher optical depth) in the innermost parts of the flow where the rapid variability is produced. The different optical depth with radius gives rise to different angular dependence of the Comptonized emission, weighting the fundamental to the inner parts of the hot flow, and the harmonic to the outer. This is the first model which can explain both the spectrum of the QPO, and its harmonic, in a self consistent geometry.

Citation

Axelsson, M., Done, C., & Hjalmarsdotter, L. (2014). An imperfect double: probing the physical origin of the low-frequency quasi-periodic oscillation and its harmonic in black hole binaries. Monthly Notices of the Royal Astronomical Society, 438(1), 657-662. https://doi.org/10.1093/mnras/stt2236

Journal Article Type Article
Acceptance Date Nov 14, 2013
Online Publication Date Dec 13, 2013
Publication Date Feb 11, 2014
Deposit Date Mar 16, 2016
Publicly Available Date Mar 28, 2024
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 438
Issue 1
Pages 657-662
DOI https://doi.org/10.1093/mnras/stt2236
Related Public URLs http://adsabs.harvard.edu/abs/2014MNRAS.438..657A

Files

Published Journal Article (778 Kb)
PDF

Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.





You might also like



Downloadable Citations