Dr. Judhajeet Basu

Novae consist of a white dwarf (WD) accreting matter from a main-sequence/evolved donor, leading to thermonuclear runaways on the WD’s surface. Novae show diversity in their lightcurves owing to the differences in the nature of the WD, the accretion rate, and the secondary. These systems provide critical insights into binary interactions, particularly in understanding potential Type Ia supernova progenitors. To gain a comprehensive understanding of these events, we survey M31 using the GROWTH India Telescope (GIT) in optical and Ultraviolet Imaging Telescope (UVIT) in FUV. While M31 and other nearby galaxies have been surveyed in optical for more than a century, UV studies remain unexplored, especially at quiescence. Our analysis of archival AstroSat UVIT data of M31 aimed to study these systems in quiescence. The most interesting among these are the rapidly recurring systems, i.e., novae, which show repeated outbursts every 10 years or less. In this context, I will discuss the multiwavelength observations of M31N 2008-12a, LMCN 1968-12a, and M31N 2017-01e. These systems show diversity in accretion channels and secondary characteristics. However, their photometric and spectroscopic evolution in X-ray, UV, and optical wavelengths points to massive WDs accreting at high rates. A key question we address is whether the massive WDs in these systems can grow to the Chandrasekhar limit and eventually explode as type Ia supernovae. In contrast, I will also discuss the GIT discovery and follow-up of the classical nova AT 2023tkw in M31, characterized by multiple lightcurve peaks. Spectroscopic and photometric evolution reveal a very contrasting nature of the binary as compared to recurrent novae. It also provides insights into the driving force behind the multiple peaks seen in the lightcurve. Through these studies, we aim to provide a comprehensive view of nova evolution, from surveys to detailed individual system analyses, highlighting the importance of multiwavelength observations in understanding these dynamic events.