An observational perspective into the nature of short-plateau Type II supernovae

Abstract

Supernovae (SNe, singular SN), the endpoints of stellar evolution, have fascinated humans since time immemorial, with recorded evidence dating back to two millennia. Continuing this quest, modern astronomy and astrophysics have come far in understanding these events and not mere recording for bookkeeping purposes. Astronomers are widely using these violent cosmic deaths in many domains of astronomy. Some common themes are to study galactic chemical evolution, measure cosmological distances independent of other measurements, study natal kicks to compact objects, e.g., white dwarfs, neutron stars, and black holes, sources of various heavier elements, and a few others. These explosions also help to understand the stellar evolution, formation of neutron stars and black holes, host environment, and mass loss mechanisms. Further, SNe are considered one of the sources of gravitational wave radiation and high-energy gamma rays. Even in interdisciplinary areas, their use is becoming eminent in studying metal enrichment in the universe and the possible effects of a nearby SN on Earth and its biosphere. Evidently, SNe play a crucial role in astrophysics, and hence their study becomes equally essential. Their studies as single events are equally important as studying them as a population. Numerous events do not fit the orthodox classification schemes and require a different explanation with thorough studies. Studying such peculiar events in great detail for better classification and judiciously weeding out contaminant sources from larger samples used in other astrophysical domains is crucial. The recent advent of extensive surveys such as All-Sky Automated Survey for Supernovae (ASASSN), Asteroid Terrestrial-impact Last Alert System (ATLAS), Zwicky Transient Facility (ZTF), etc., have led to numerous discoveries, and upcoming surveys like Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) would only add more. These require detailed spectroscopic and multi-band photometric follow-up for a clear understanding. The James Webb Space Telescope (JWST) has recently opened up the SNe domain to much higher redshifts. Apart from their observational studies, it is critical to model these events with the existing tools to get a detailed picture of them. Only with enough observations, analysis, and modeling of these events could we get much information about them. Studying these single events in great detail is necessary to gather better statistics and say more about different trends in these populations. Hence, we take up this work to observe, analyze, and model such explosions in detail to improve our understanding using observation facilities available in national and international domains. We attempt to analyze and model these events for in-depth understanding using open-source tools as widely as possible. The thesis is focused on the rarely occurring Type IIP supernovae with shorter plateau duration in their light curve evolution. Various modeling works have theorized that these events could originate from higher-mass red supergiants (RSGs). In this work, we study and understand several short-plateau Type II SNe in detail using multiwavelength observation and 1-D hydrodynamical modeling. It has enabled us to show alternate origins of these events based on observational evidence backed by detailed modeling of these rare events. Further, a great deal of diversity has also been revealed among these events. The thesis makes use of various national and international observational facilities, both ground and space-based, such as in optical 2-m Himalayan Chandra Telescope, 0.7-m GROWTH India Telescope, in ultraviolet AstroSat, Swift/UVOT and 1.5-m near-infrared KANATA telescope from Japan. Other publicly available data are also used whenever available. We have used various analytical and modeling tools to estimate several explosion parameters and attempted to know about the progenitor and its properties. The thesis presents detailed studies of SN 2018gj, SN 2020jfo, and SN 2021wvw short plateau SNe, including SN 2023ixf, the nearby decadal supernova.