A strongly truncated inner accretion disc in the Rapid Burster
Publication date: 01 March 2017
Authors: van den Eijnden, J., et al.
Journal: MNRAS
Volume: 466
Issue: 1
Page: L98-L102
Year: 2017
Copyright: © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Published online: 5 December 2016
The neutron star (NS) low-mass X-ray binary (LMXB) the Rapid Burster (RB; MXB 1730-335) uniquely shows both Type I and Type II X-ray bursts. The origin of the latter is ill-understood but has been linked to magnetospheric gating of the accretion flow. We present a spectral analysis of simultaneous Swift, NuSTAR and XMM-Newton observations of the RB during its 2015 outburst. Although a broad Fe K line has been observed before, the high quality of our observations allows us to model this line using relativistic reflection models for the first time. We find that the disc is strongly truncated at 41.8+6.7-5.3 gravitational radii (~87 km), which supports magnetospheric Type II burst models and strongly disfavours models involving instabilities at the innermost stable circular orbit. Assuming that the RB magnetic field indeed truncates the disc, we find B = (6.2 ± 1.5) × 108 G, larger than typically inferred for NS LMXBs. In addition, we find a low inclination (i=29°±2°). Finally, we comment on the origin of the Comptonized and thermal components in the RB spectrum.
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