Probing the effects of a thermonuclear X-ray burst on the neutron star accretion flow with NuSTAR
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Author(s)
Degenaar, N.
Koljonen, K. I. I.
Kara, E.
Altamirano, D.
Miller, J. M.
Fabian, A. C.
Chakrabarty, Deepto
Date Issued
January 2016
Journal
Monthly Notices of the Royal Astronomical Society
Publisher
Oxford University Press
Citation
Degenaar, N., K. I. I. Koljonen, D. Chakrabarty, E. Kara, D. Altamirano, J. M. Miller, and A. C. Fabian. “Probing the Effects of a Thermonuclear X-Ray Burst on the Neutron Star Accretion Flow withNuSTAR.” Monthly Notices of the Royal Astronomical Society 456, no. 4 (January 14, 2016): 4256–4265. © 2016 The Authors
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Author's final manuscript
Abstract
Observational evidence has been accumulating that thermonuclear X-ray bursts ignited on the surface of neutron stars influence the surrounding accretion flow. Here, we exploit the excellent sensitivity of NuSTAR up to 79 keV to analyse the impact of an X-ray burst on the accretion emission of the neutron star LMXB 4U 1608−52. The ≃200 s long X-ray burst occurred during a hard X-ray spectral state, and had a peak intensity of ≃30–50 per cent of the Eddington limit with no signs of photospheric radius expansion. Spectral analysis suggests that the accretion emission was enhanced up to a factor of ≃5 during the X-ray burst. We also applied a linear unsupervised decomposition method, namely non-negative matrix factorization (NMF), to study this X-ray burst. We find that the NMF performs well in characterizing the evolution of the burst emission and is a promising technique to study changes in the underlying accretion emission in more detail than is possible through conventional spectral fitting. For the burst of 4U 1608−52, the NMF suggests a possible softening of the accretion spectrum during the X-ray burst, which could potentially be ascribed to cooling of a corona. Finally, we report a small (≃3 per cent) but significant rise in the accretion emission ≃0.5 h before the X-ray burst, although it is unclear whether this was related to the X-ray burst ignition.
MIT Department
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.1093/mnras/stv2965
