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Probing the effects of a thermonuclear X-ray burst on the neutron star accretion flow with NuSTAR

Probing the effects of a thermonuclear X-ray burst on the neutron star accretion flow with NuSTAR
Probing the effects of a thermonuclear X-ray burst on the neutron star accretion flow with NuSTAR
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.
0035-8711
4256-4265
Degenaar, N.
54149051-d74e-4e43-a7cd-501ec4023511
Koljonen, K.I.I.
ca7f5775-3ec7-484e-9f47-69b2dc31d0bf
Chakrabarty, D.
f70eba21-20cc-4f7f-87b3-ccd8716ddea1
Kara, E.
be56e1e8-9ba9-4c2a-838c-63fdc344e911
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
Miller, J.M.
078305f0-03c7-4982-95ff-a92bc2f75b54
Fabian, A.C.
0c353376-f159-4129-b03e-d3993c0c5406
Degenaar, N.
54149051-d74e-4e43-a7cd-501ec4023511
Koljonen, K.I.I.
ca7f5775-3ec7-484e-9f47-69b2dc31d0bf
Chakrabarty, D.
f70eba21-20cc-4f7f-87b3-ccd8716ddea1
Kara, E.
be56e1e8-9ba9-4c2a-838c-63fdc344e911
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
Miller, J.M.
078305f0-03c7-4982-95ff-a92bc2f75b54
Fabian, A.C.
0c353376-f159-4129-b03e-d3993c0c5406

Degenaar, N., Koljonen, K.I.I., Chakrabarty, D., Kara, E., Altamirano, D., Miller, J.M. and Fabian, A.C. (2016) Probing the effects of a thermonuclear X-ray burst on the neutron star accretion flow with NuSTAR. Monthly Notices of the Royal Astronomical Society, 456 (4), 4256-4265. (doi:10.1093/mnras/stv2965).

Record type: Article

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.

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Probing the effects of a thermonuclear X-ray burst on the neutron star accretion flow with NUSTAR.pdf - Accepted Manuscript
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Accepted/In Press date: 16 December 2015
e-pub ahead of print date: 13 January 2016
Published date: 11 March 2016
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 394809
URI: http://eprints.soton.ac.uk/id/eprint/394809
ISSN: 0035-8711
PURE UUID: e1e71a3b-9ec9-4556-a033-a844059c3578
ORCID for D. Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 24 May 2016 10:56
Last modified: 17 Dec 2019 01:35

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