Transients provide a window into some of the most energetic and rapidly evolving processes in the Universe. Among these, circumstellar material (CSM)-interacting transients are powered by shocks generated when explosive or eruptive outflows encounter the surrounding CSM, producing diverse observational signatures across the electromagnetic spectrum. This thesis investigates these phenomena through their detection, characterization, and detailed photometric and spectroscopic analysis.
The thesis presents a comprehensive UV–optical–near-infrared (NIR) photometric and spectroscopic study of three CSM-interacting supernovae (SNe): ASASSN-14il, SN 2021foa, and SN 2024kgi. Their light curves are modelled using semi-analytical and radiation-hydrodynamic methods, including a new semi-analytical treatment of the evolving photon-diffusion timescale associated with propagating shock fronts. The inferred mass-loss rates of approximately 0.1–7 M☉ yr⁻¹ substantially exceed those expected from conventional line-driven stellar winds, favouring eruptive and/or binary-driven mass-loss mechanisms. Spectroscopic analyses confirm hydrogen- and helium-rich CSM and reveal asymmetries that may indicate binary influence. SN 2021foa exhibits properties intermediate between the H-rich Type IIn and He-rich Type Ibn classes, supporting a continuum in CSM composition and mass-loss evolution. SN 2024kgi shows an NIR echo from pre-existing CSM dust, while ASASSN-14il and SN 2024kgi show evidence of post-shock dust formation. These findings highlight the limitations of standard stellar-evolution models in explaining extreme mass-loss episodes and underscore the potential importance of eruptive and binary-influenced processes.
The thesis also contributes to the data-processing pipeline of the 4-m International Liquid Mirror Telescope (ILMT), a survey facility designed for long-term monitoring of transient sources. A modern pipeline was developed for accurate aperture and point-spread-function (PSF) photometry, accounting for spatial variations in the PSF across the field of view. Contributions were also made to the astrometric pipeline.
Overall, this work demonstrates the importance of combining early transient detection with long-term, multi-wavelength photometric and spectroscopic monitoring to investigate the mass-loss histories and circumstellar environments of massive stars.
Mr. Naveen Dukiya is a Senior Project Associate at ARIES, working under the supervision of Dr. Kuntal Misra. He is pursuing his PhD at Mahatma Jyotiba Phule Rohilkhand University, Bareilly, under the co-supervision of Prof. Archana Gupta. This seminar is part of his pre-thesis submission.
