Understanding the orbital dynamics of X-ray binaries with AstroSat

The evolutionary processes in X-ray binaries are driven by various physical mechanisms, with conservative mass transfer being the major influencer, which leads to the redistribution of angular momentum, thereby impacting the orbital dynamics. On top of this, a non-conservative mass transfer due to various radiative processes can also alter the momentum distribution within these systems. Highlighting the timing capabilities of AstroSat, I will talk about novel findings in two XRBs – the evolution of orbital decay rate in HMXB LMC X-4 and the jittery behaviour of eclipse arrival times in LMXB XTE J1710-281. In LMC X-4, with AstroSat data, the existence of second derivative of the orbital period has been confirmed for first time ever in an accreting X-ray pulsar system. The orbital evolution in XTE J1710-281 has two statistically equivalent interpretations - either presence of four distinct epochs of orbital period in this system or presence of a massive circum-binary object around the binary. In the light of these results, I will provide a comprehensive overview on our current understanding of various physical mechanisms possible for driving the orbital evolution in these systems. (Ref. Jain, C. et. al., MNRAS, 2024, 529, 4, 4056) (Ref. Jain, C. et. al., MNRAS, 2022, 517, 2, 2131)