High Energy Astrophys. & Astropart. Phys (API, FNWI), Faculty of Science, Parker, Michael [0000-0002-8466-7317], Fabian, Andrew [0000-0002-9378-4072], Apollo - University of Cambridge Repository
المصدر:
Monthly Notices of the Royal Astronomical Society: Letters, 466(1), L98-L102. Oxford University Press
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 $\textit{Swift}$, $\textit{NuSTAR}$ and $\textit{XMM–Newton}$ 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 $\textit{B}$ = (6.2 ± 1.5) × 10$^{8}$ G, larger than typically inferred for NS LMXBs. In addition, we find a low inclination ($\textit{i}$=29$^{\circ}$±2$^{\circ}$). Finally, we comment on the origin of the Comptonized and thermal components in the RB spectrum. We thank the referee for comments on this Letter. JvdE and ND are supported by a Vidi grant from the Netherlands Organization for Scientific Research (NWO) awarded to ND. ND also acknowledges support via a Marie Curie fellowship (FP-PEOPLE-2013-IEF-627148) from the European Commission. ACF, AL and MP are supported by Advanced Grant Feedback 340442 from the European Research Counsil (ERC). TB acknowledges support from NewCompStar (COST Action MP1304). JvdE and TB acknowledge the hospitality of the Institute of Astronomy in Cambridge, where this research was carried out.
