Thermonuclear X-ray bursts in rapid succession in 4U 1636-536 with AstroSat-LAXPC

Abstract

We present results from an observation of the low-mass X-ray binary 4U 1636-536 obtained with the LAXPC instrument aboard AstroSat. The observations of 4U 1636-536 made during the performance verification phase of AstroSat showed seven thermonuclear X-ray bursts in a total exposure of ˜65 ks over a period of about two consecutive days. Moreover, the light curve of 4U 1636-536 revealed the presence of a rare triplet of X-ray bursts, having a wait time of about 5.5 min between the second and the third bursts. We also present results from time-resolved spectroscopy performed during these seven X-ray bursts. In addition, we have also detected a transient quasi-periodic oscillation at ˜5 Hz. However, we did not find any evidence of kilo-hertz quasi-periodic oscillations and/or X-ray burst oscillations, perhaps due to the hard spectral state of the source during this observation.