| Authors : | Manoneeta Chakraborty [presenter], Tolga Guver [first author], Z. Funda Bostanci, Tugba Boztepe, Ersin Gogus , Peter Bult, Unnati Kashyap, David R. Ballantyne, R. M. Ludlam, C. Malacaria , Gaurava K. Jaisawal, Tod E. Strohmayer, Sebastien Guillot, and Mason Ng |
| Abstract : | Intense X-ray bursts (type-I bursts), originating from unstable thermonuclear conflagration on the surface of neutron star low-mass X-ray binaries (LMXBs), can offer a promising tool to constrain the equation of state of the supra-nuclear matter at the neutron star core and to probe gravity in the strong field regime near the neutron star. In order to employ the bursts to investigate the neutron star characteristics, the burst spectral properties and their evolution must be understood in detail. Here, we present the detection of 51 thermonuclear X-ray bursts observed from neutron star LMXB (low mass X-ray binary) 4U 1636–536 by the Neutron Star Interior Composition Explorer (NICER) over the course of a 3 yr monitoring campaign. We performed the time-resolved spectroscopy for 40 of these bursts and showed the existence of a strong, soft excess in all the burst spectra above the typical thermal emission. The excess emission can be explained by the use of a scaling factor (the fa method) to the persistent emission of the source, which is attributed to the increased mass accretion rate onto the neutron star due to Poynting–Robertson drag. The soft excess emission can also be characterized by the use of a model taking into account the reflection of the burst emission off the accretion disk. We also present the time-resolved spectral analysis of five X-ray bursts simultaneously observed by NICER and AstroSat, which confirm the main results with even greater precision. Finally, we present evidence for Compton cooling using seven X-ray bursts observed contemporaneously with NuSTAR, by means of a correlated decrease in the hard X-ray light curve of 4U 1636–536 as the bursts start. |
