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A Systematic Study of Variability in a Sample of Ultraluminous X-ray Sources

Heil, L.M.; Vaughan, S.; Roberts, T.P.

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L.M. Heil

S. Vaughan


We present results from a study of short-term variability in 19 archival observations by XMM–Newton of 16 ultraluminous X-ray sources (ULXs). Eight observations (six sources) showed intrinsic variability with power spectra in the form of either a power-law or broken power-law-like continuum and in some cases quasi-periodic oscillations (QPOs). The remaining observations were used to place upper limits on the strength of possible variability hidden within. Seven observations (seven sources) yielded upper limits comparable to, or higher than, the values measured from those observations with detectable variations. These represented the seven faintest sources, all with fx < 3 × 10−12 erg cm−2 s−1. In contrast, there are four observations (three sources) that gave upper limits significantly lower than both the values measured from the ULX observations with detectable variations, and the values expected by comparison with luminous Galactic black hole X-ray binaries (BHBs) and active galactic nuclei (AGN) in the observed frequency bandpass (10−3–1 Hz). This is the case irrespective of whether one assumes characteristic frequencies appropriate for a stellar mass (10 M⊙) or an intermediate mass (1000 M⊙) black hole, and means that in some ULXs the variability is significantly suppressed compared to bright BHBs and AGN. We discuss ways to account for this unusual suppression in terms of both observational and intrinsic effects and whether these solutions are supported by our results.


Heil, L., Vaughan, S., & Roberts, T. (2009). A Systematic Study of Variability in a Sample of Ultraluminous X-ray Sources. Monthly Notices of the Royal Astronomical Society, 397(2), 1061-1072.

Journal Article Type Article
Publication Date Aug 1, 2009
Deposit Date Feb 19, 2014
Publicly Available Date Feb 20, 2014
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 397
Issue 2
Pages 1061-1072
Keywords Black hole physics, X-rays, Binaries, Galaxies.


Published Journal Article (796 Kb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2009 The Authors. Journal compilation © 2009 RAS. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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