Indian Astronomers Use AstroSat to Reveal Features of X-Ray Binary System

Astronomers from India have observed an X-ray binary system in space, known as GRS 1915+105, using the AstroSat, the first dedicated Indian astronomy mission. At a distance of some 28,000 light-years away from the Earth, this system is a superluminal low-mass X-ray binary (LMXB). It was first detected in August 1992. But AstroSat observations confirmed it exhibits various types of variability classes. It can transition from one class to another within just a few hours. The system has an orbital period, the time it takes to complete one revolution, of 33.5 days.

Its black hole is estimated to be around 13 times more massive than the Sun. X-ray binary (XRB) systems comprise a normal star or a white dwarf transferring mass onto a small neutron star or a black hole. Based on the mass of the companion star, XRBs are classified as low-mass X-ray binaries (LMXBs) and high-mass X-ray binaries (HMXBs).

Astronomers found the X-ray intensity variations of GRS 1915+105 resembled the light curve of a “canonical” outbursting black hole. However, they also found that this system does not follow the exemplary ‘q’-diagram in the hardness-intensity diagram (HID), unlike canonical sources, according to a report on Phys.org, an online science, research, and technology news aggregator.

Previous observations have shown that GRS 1915+105 displays diverse variability in its light curve — 15 classes so far. To learn more about the system, a team of astronomers led by Athulya Menon of Dayananda Sagar University, Bengaluru, decided to investigate the source with AstroSat.

“In this paper, we perform an in-depth analysis of 31 AstroSat observations of GRS 1915+105 during the period of November 2016 to June 2019 by studying the broadband ‘spectro-temporal’ features of the source,” the researchers stated.

According to them, the behaviour of GRS 1915+105 indicates it will evolve towards an obscured low-luminosity phase, with a decrease in the intrinsic bolometric luminosity of the source due to obscuration.