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

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 analyze 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.

10 pages, 10 figures, 1 table, to appear in MNRAS

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• Accretion disk signatures in Type I X-ray Bursts: prospects for future missions
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• The study of thermonuclear X-ray bursts in accreting millisecond pulsar MAXI J1816-195 with NuSTAR and NICER
• A catalog of intermediate duration Type I X-ray bursts observed with the INTEGRAL satellite
• Insight-HXMT observations on thermonuclear X-ray bursts from 4U~1608--52 in the low/hard state: the energy-dependant hard X-ray deficit and cooling saturation of the corona
• AstroSat observation of rapid Type-I thermonuclear burst from the low mass X-ray binary GX 3+1
• Detection of the thermonuclear X-ray bursts and dips from the X-ray binary 4U 1323-62 with AstroSat/LAXPC
• Thermonuclear Type-I X-ray Bursts and Burst Oscillations from the Eclipsing AMXP Swift J1749.4-2807
• The X-ray bursts within the 2010 outburst of the accreting millisecond X-ray pulsar SAX J1748.9-2021
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• NuSTAR and AstroSat observations of thermonuclear X-ray bursts with short-recurrence times in 4U 1636$-$536