Broad-band time-resolved spectroscopy of thermonuclear X-ray bursts from 4U 1636-536 using AstroSat

Abstract

Broad-band spectral studies of type I X-ray bursts can put strong constraints on the physics of burst spectra as well as their interaction with the environment. We present the results obtained from the broad-band time-resolved spectroscopy of 15 thermonuclear bursts detected simultaneously from the neutron star atoll source 4U 1636-536 using the Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) onboard AstroSat. During the observations with AstroSat, the low-mass X-ray binary 4U 1636-536 is observed to show a modest spectral evolution within the island state. The broad-band burst spectra are observed to show an excess in addition to the thermal emission from the neutron star surface near the peak of the bursts. We investigate the interpretation of the excess observed near the peak of the burst as re-emission/reprocessing of the photons by the accretion disc/corona or scattering of the photons in the neutron star atmosphere or the enhanced persistent emission due to the Poynting-Robertson drag. This is the first reported broad-band simultaneous study of type I bursts using LAXPC and SXT onboard AstroSat. This kind of study may provide a better understanding of the burst-accretion interaction and how the bursts influence the overall accretion process contributed by the accretion disc as well as the corona. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.