Cookies

We use cookies to ensure that we give you the best experience on our website. By continuing to browse this repository, you give consent for essential cookies to be used. You can read more about our Privacy and Cookie Policy.


Durham Research Online
You are in:

The X-ray spectral evolution of the ultraluminous X-ray source Holmberg IX X-1.

Luangtip, W. and Roberts, T. P. and Done, C. (2016) 'The X-ray spectral evolution of the ultraluminous X-ray source Holmberg IX X-1.', Monthly notices of the Royal Astronomical Society., 460 (4). pp. 4417-4432.

Abstract

We present a new analysis of X-ray spectra of the archetypal ultraluminous X-ray source (ULX) Holmberg IX X-1 obtained by the Swift, XMM–Newton and NuSTAR observatories. This ULX is a persistent source, with a typical luminosity of ∼1040 erg s−1, that varied by a factor of 4–5 over eight years. We find that its spectra tend to evolve from relatively flat or two-component spectra in the medium energy band (1–6 keV), at lower luminosities, to a spectrum that is distinctly curved and disc-like at the highest luminosities, with the peak energy in the curved spectrum tending to decrease with increased luminosity. We argue that the spectral evolution of the ULX can be explained by super-Eddington accretion models, where in this case we view the ULX down the evacuated funnel along its rotation axis, bounded by its massive radiatively driven wind. The spectral changes then originate in enhanced geometric beaming as the accretion rate increases and wind funnel narrows, causing the scattered flux from the central regions of the supercritical flow to brighten faster than the isotropic thermal emission from the wind, and so the curved hard spectral component to dominate at the highest luminosities. The wind also Compton down-scatters photons at the edge of the funnel, resulting in the peak energy of the spectrum decreasing. We also confirm that Holmberg IX X-1 displays spectral degeneracy with luminosity, and suggest that the observed differences are naturally explained by precession of the black hole rotation axis for the suggested wind geometry.

Item Type:Article
Full text:(VoR) Version of Record
Download PDF
(1729Kb)
Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1093/mnras/stw1282
Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:26 May 2016
Date deposited:28 July 2016
Date of first online publication:30 May 2016
Date first made open access:28 July 2016

Save or Share this output

Export:
Export
Look up in GoogleScholar