| Authors : | Unnati Kashyap, Department of Astronomy, Astrophysics, and Space Engineering (DAASE), Indian Institute of Technology Indore, Khandwa Road, Simrol, Indore 453552, Madhya Pradesh, India;
Biki Ram, Department of Astronomy, Astrophysics, and Space Engineering (DAASE), Indian Institute of Technology Indore, Khandwa Road, Simrol, Indore 453552, Madhya Pradesh, India;
Tolga Güver, Department of Astronomy and Space Sciences, Science Faculty, Istanbul University, Beyazıt, 34119 İstanbul, Turkey; Istanbul University Observatory Research and Application Center, Istanbul University, 34119 İstanbul, Turkey;
Manoneeta Chakraborty, Department of Astronomy, Astrophysics, and Space Engineering (DAASE), Indian Institute of Technology Indore, Khandwa Road, Simrol, Indore 453552, Madhya Pradesh, India |
| Abstract : | Thermonuclear X-ray bursts (Type-I) occur due to the unstable burning of accreted hydrogen/helium on the surface of the neutron star in accreting Low Mass X-ray Binaries (LMXBs). The physics behind the Type I X-ray burst is complex, and broadband studies can put strong constraints on the physics of burst spectra and their interaction with the binary environment, consequently on the neutron star radius. Although, time-resolved studies of thermonuclear bursts show that the burst spectra can be described by evolving Planckian functions with temperatures ranging from 1 to 3 keV but deviations from the standard Planckian model have also been reported in many recent studies. I will be presenting the broadband time-resolved spectroscopy study of 15 thermonuclear bursts detected simultaneously from the neutron star atoll X-ray binary 4U 1636-536 using LAXPC and SXT onboard AstroSat. The Low mass X-ray binary 4U 1636-536 shows a modest continuum spectral evolution within the island state of its atoll track during these observations. In our analysis, the broadband burst spectra show a strong excess besides the thermal emission from the neutron star surface, especially near the peak of the bursts which is not generally identifiable statistically. We discuss the interpretation of the excess detected near the burst peak as re-emission/reprocessing of the photons by the accretion disk/corona or scattering of the photons in the neutron star atmosphere or enhancement of the accretion flow due to the Poynting-Robertson (PR) radiation drag on the disk. This is the first reported broad-band simultaneous study of thermonuclear bursts using LAXPC and SXT onboard AstroSat. This study provides a deeper insight into the burst feedback on the accretion process and the burst-accretion interactions.
(Kashyap et al., MNRAS, Volume 509, Issue 3, January 2022, Pages 3989–4007; https://doi.org/10.1093/mnras/stab2838) |
