Unveiling diverse nature of core collapse supernovae

Abstract

Core-collapse supernovae (CCSNe) are catastrophic astrophysical phenomena that occur during the last evolutionary stages of massive stars having initial masses ≳ 8 M⊙. These catastrophic events play a pivotal role in enriching our Universe with heavy elements and are also responsible for the birth of Neutron stars and stellar mass Black holes. Knowledge of the possible progenitors of CCSNe is fundamental to understanding these transient events. Additionally, the underlying circumstellar environment around possible progenitors and the physical mechanism powering the light curves of these catastrophic CCSN events also require careful investigations to unveil their nature. Based on the spectroscopic observational features, the CCSNe are primarily divided into H-rich and Hdeficient categories. The H-rich CCSNe display unambiguous H-features in their spectra, while H-deficient CCSNe don’t. Type Ib SNe are a subclass of H-deficient CCSNe that lack prominent H-features in their spectra but display distinct He-feature. The research work within the context of the present thesis is an attempt to investigate the possible progenitors, ambient media around the progenitors, and powering mechanisms behind the light curve of CCSNe. Particularly, fractional contributions of different elements, including hydrogen, the key element discriminating Type Ib and Type IIb SNe, are studied in detail. We also employed several powering mechanisms to decipher underlying physical mechanisms behind Type Ib and Type IIb SNe. We have employed observational data from several telescopes, state-of-the-art simulation modules, and 1-dimensional hydrodynamic codes for such investigations. In this thesis, we have investigated the photometric and spectroscopic properties of two Type Ib CCSNe, namely, SN 2015ap and SN 2016bau. We aim to gain insight into their possible progenitors, the circumstellar environment surrounding them, and the powering mechanism for their light curve. We have analysed the photometric characteristics of the CCSNe mentioned above, encompassing their colour evolution, bolometric luminosity, photospheric radius, temperature, and velocity evolution. By analysing their light curves, we have computed the ejecta mass, synthesised nickel mass, and ejecta kinetic energy. Thus, the time domain astronomy of CCSNe is crucial to get insight into their several physical properties. Furthermore, we have modelled the spectra of SN 2015ap and SN 2016bau at different stages of their development and also compared their spectra with several other similar SNe. The P Cygni profiles of different lines present in the spectra are utilised to understand the velocity evolution of several line-emitting regions. The 1- dimensional stellar modelling of the possible progenitors and the comparison of the results of synthetic hydrodynamic explosions with actual observations indicate a 12 M⊙ progenitor exploding in a solar metallicity region as the potential progenitor for SN 2015ap. In contrast, a slightly less massive star exploding in a solar metallicity environment is the expected progenitor for SN 2016bau. At the pre-SN stage, the mass of the progenitor of SN 2016bau lies close to the boundary between the SN and a non-SN phase. Type IIb SNe are another subclass of CCSNe and are thought to bridge the gap between H-rich and H-deficient CCSNe. At first, their spectra reveal noticeable H-features, but after a few weeks, the H-features diminish while prominent He-features begin to emerge. Type Ib/IIb CCSNe progenitors retain no to very small amounts of hydrogen during their explosions. However, the correct estimation of the amount of hydrogen retained before explosion by the underlying CCSN progenitor is subjected to contamination by the uncertainties associated with determining the extinction and distance of the CCSN. The photometric and spectroscopic investigations of Type IIb CCSNe are necessary to understand their progenitors, ambient medium, and powering mechanisms. Such analyses also decipher their link with the H-rich and H-deficient CCSNe. In the present research work, we have performed the photometric and spectroscopic investigation of a Type IIb SN 2016iyc. Our findings indicate that SN 2016iyc lies towards the lower end of the distribution compared to similar CCSNe in terms of inherent brightness. The light curve analysis indicates that SN 2016iyc produces a relatively smaller amount of ejecta mass and suffers low nickel mass production. Based on the photometric and spectroscopic behaviour of SN 2016iyc, we performed the stellar evolution of models having initial zero-age main-sequence (ZAMS) masses in the range of 9–14 M⊙. The synthetic explosions of ZAMS star models with mass in the range of 12– 13 M⊙ having the pre-SN radius, R0 within (240–300) R⊙, produce bolometric luminosity light curves and photospheric velocities that match well with actual observations. Additionally, ejecta mass Mej = (1.89–1.93) M⊙, explosion energy Eexp = (0.28–0.35) ×1051 erg, and MNi < 0.09 M⊙, are in good agreement with observed estimations; thus, SN 2016iyc probably exploded from a progenitor lying towards the lower mass limits for SNe IIb. Additional hydrodynamic simulations have also been conducted to investigate the explosions of SN 2016gkg and SN 2011fu, aiming to compare intermediate- and high-luminosity examples among the extensively studied SNe Type IIb. The results obtained from modelling the potential progenitors and simulating the explosions of SN 2016iyc, SN 2016gkg, and SN 2011fu reveal a range of progenitor masses for SNe IIb. The range of progenitor masses for Type IIb SNe identified under the present research work lies well within the established range of progenitor masses for CCSNe. After discussing the properties of H-deficient SNe and the behaviour of a Type IIb SN retaining an intermediate amount of H-envelope, we provide interesting properties of H-rich and H-deficient SNe together that originate from progenitors, each having a mass of 25 M⊙ at ZAMS and zero metallicity. CCSNe from massive Population III (Pop III) stars are thought to have had an enormous impact on the early Universe. The SNe from Pop III stars were responsible for the initial enrichment of the early Universe with heavy elements. Pop III stars played a key role in cosmic re-ionization. Thus, the investigations of the stellar evolution of Pop III stars and resulting SNe are essential. This thesis presents the results of 1-dimensional stellar evolution simulations of a rotating Pop III star having an initial mass of 25 M⊙. Starting from ZAMS, the models are evolved until the onset of core collapse. The rapidly rotating models exhibit violent and intermittent mass loss episodes following the main sequence stage. Notably, the Pop III models exhibit smaller pre-SN radii compared to the model with solar metallicity. Further, with models at the stage of the onset of core collapse, we perform the hydrodynamic simulations of the resulting SNe. As a consequence of the mass losses due to corresponding rotations and stellar winds, the resulting SNe span a class from weak H-rich to H-deficient CCSNe. This analysis demonstrates the substantial influence of initial stellar rotation on the evolution of massive stars and their resulting transients. Additionally, we observe that the absolute magnitudes of CCSNe originating from Pop III stars are much fainter compared to the ones originating from the star with solar metallicity. Based on the outcomes of our simulations, we conclude that within the range of explosion energies and nickel masses considered, these transient events exhibit very low luminosities. Consequently, detecting them at high redshifts would be a significant challenge. Beyond discussing the CCSNe resulting from progenitors having ZAMS masses of 25 M⊙ or less, we have also studied the stellar evolution of a massive 100 M⊙ ZAMS star up to the onset of core collapse. Based on initial mass, mass loss rate, rotation and metallicity, the resulting transient could fall into any category, PISN, PPISN, Type IIPlike SNe, and several H-rich/H-deficient SNe showing ejecta-CSM interaction signatures. However, in the presented thesis, we have investigated the consequences of a non-rotating 100 M⊙ ZAMS progenitor exploding into Type IIP-like CCSNe. We also have explored the effect of the variation of explosion energy and nickel mass on the light curves of resulting CCSNe. The research work presented here has paved the way for new avenues of exploration within astronomy and astrophysics. Ultimately, we summarise our significant findings and discuss the potential prospects. We attempt to highlight the role of observations and simulations in synergistic investigations of transients. The increasing number of progenitor detections in high-resolution pre-explosion images and further refinement of available state-of-the-art stellar evolution codes would certainly protrude the knowledge of CCSNe.