Energetic cosmic transients in the context of gamma ray bursts supernovae connections

Abstract

Supernovae (SNe) and Gamma-Ray Bursts (GRBs) are among the brightest and most energetic explosions in the Universe. There are numerous direct and indirect evidences of connections between these two di erent types of transients, particularly long GRBs (LGRBs) and stripped-envelope SNe (SESNe). In support of direct evidences, to date, more than fty LGRBs have been discovered with signatures of associated SNe (GRBSNe) in the form of the blackbody component, late-time re-brightening and broad spectral features. On the other hand, indirect evidences of SESNe and LGRB connections include the similarity among their underlying power sources, progenitors and host environments. Most of the hydrogen-de cient superluminous SNe (SLSNe-I) and LGRBs are thought to be powered by the central engine based power sources (millisecond magnetar or black hole). In addition, the progenitors and host properties of SLSNe-I are also similar to some extent to those of LGRBs, signifying the connections between these two rare classes of transients. At the same time, connections observed between ultra-long GRB 111209A and SLSN 2011kl have devised further opportunities to look for what fraction of SLSNe-I are associated with LGRBs. Besides this, some SNe-Ib (SESNe with lack of helium features in their near-peak spectra) are also suspected of being governed by central engine power sources (e.g., SN 2005bf); hence, investigating their possible connections with LGRBs is a must. This thesis examines di erent types of SESNe (SLSNe-I, a SN-Ib governed by the central engine power source and GRB-SNe) and attempts to further our understanding of the GRB-SNe connections by probing their underlying power sources, progenitors and host environments. In addition, the calibration and characterisation results of the 4K 4K CCD Imager, a rst light axial port instrument at the 3.6 m Devasthal Optical Telescope (DOT) and its importance in observing time-critical events considering the longitudinal advantage of India are also demonstrated. Our investigations include the photometric and spectroscopic studies of slow- and fastevolving SLSNe-I (SN 2010kd at z = 0.101 and SN 2020ank at z = 0.248, respectively). The semi-analytical light-curve modelling using the MINIM code indicates millisecond magnetars as possible power sources for both these events. The atter line velocities in the case of SN 2010kd and observed excess UV ux near the peak for SN 2020ank also support the central engine based power sources, which suggest similarity among the power sources of SLSNe-I and LGRBs. In the case of SN 2010kd, [O i] 6300, 6364 line luminosity suggests an upper limit of oxygen ejected mass of <10 M , which indicates the possibility of a massive progenitor (<40 M ). A massive progenitor of SN 2010kd favours an indirect link between SLSNe-I and LGRBs. A systematic comparison of the nebular spectra of SN 2010kd obtained using 8{10 m class telescopes with those of GRB-SNe revealed that they have similar spectral lines with di erent intensities, possibly providing clues of variations in their physical conditions (for the same progenitor system) and/or explosion mechanisms of central-engine-driven LGRBs. Using the rest-frame UV ux, and [O iii]/H and [Nii]/H ux ratios, we contend that the host of SN 2010kd is a dwarf galaxy that exhibits a low-luminosity and a high star-formation rate similar to those of hosts of LGRBs. In addition, the photometric and spectroscopic analysis of SN 2010kd and SN 2020ank also help to constrain numerous physical parameters important in understanding the nature of such energetic transients in more detail. This work also investigates the photometric, polarimetric and spectroscopic studies of SN 2012au, one of the most bright, slow-decaying and energetic SNe-Ib. Light-curve modelling insinuates a magnetar as a likely powering source for SN 2012au. Additionally, the consistency of the late-time light curve of SN 2012au with the standard magnetic dipole equation, and results from MESA and SNEC also support a magnetar powering mechanism for SN 2012au. Imaging polarisation values and spectral lines shape in the nebular phase spectra of SN 2012au favour asphericity and/or clumpiness in the ejecta. The absence of the rst overtone of CO in the NIR spectra of SN 2012au suggests strong mixing of ionised helium between ejecta layers. Our spectral analysis indicates that the progenitor of SN 2012au exhibits oxygen, helium-core and zero-age-main-sequence masses of 1.62 0.15, 4{8 and 17{25 M , respectively. In addition, SN 2012au appears to originate from a single massive Wolf-Rayet star which is also among the possible progenitors for LGRBs. A central engine-based powering source and asphericity in the ejecta, along with higher values of physical parameters like expansion velocity, kinetic energy, ejecta mass and progenitor mass than other SNe-Ib/Ic but comparable to those observed for GRB-SNe strongly support resemblance between SN 2012au and GRB-SNe. This thesis presents late-time optical follow-up observations and interpretation of GRB 171010A/SN 2017htp (z = 0.33) and low-luminosity GRB 171205A/SN 2017iuk (z = 0.037) along with the prompt emission data analysis of these two LGRBs associated with SESNe. The prompt characteristics such as spectral hardness, T90 (the period over which 90% of the entire background-subtracted counts are observed) and minimum variability time-scale are comparable for both the bursts. The isotropic X{ray and kinetic energies of the plateau phase of GRB 171205A are found to be less than the maximum energy budget of magnetars, supporting magnetar as a central engine powering source. The new late-time optical data of SN 2017htp and SN 2017iuk observed using the 4K 4K CCD Imager at the 3.6 m DOT, along with published ones, indicate that SN 2017htp is one of the brightest and SN 2017iuk is among the faintest GRB-SNe. Semi-analytical light-curve modelling of SN 2017htp, SN 2017iuk and only known ultra-long GRB 111209A associated superluminous supernova (SLSN 2011kl) are performed using the MINIM code. The model with a spin-down millisecond magnetar as a central engine powering source nicely reproduced the bolometric light curves of all three GRB-SNe mentioned above. The magnetar central engines for SN 2017htp, SN 2017iuk and SLSN 2011kl exhibit values of initial spin periods higher and magnetic elds closer to those observed for LGRBs and SLSNe-I. Deeper detection of these rare events at such late epochs also demonstrates the capabilities of the 3.6 m DOT for deep imaging considering longitudinal advantage in the era of time-domain astronomy in the coming years. As a part of astronomical instrumentation related activities under the present work, this thesis discusses the recent characterisation results of the 4K 4K CCD Imager, a rst light axial-port instrument of the 3.6 m DOT. It also presents the photometric calibrations and measurements of the extinction coe cients and night-sky brightness values at the 3.6m DOT site, based on the imaging data taken between 2016 March and 2021 February. For the 4K 4K CCD Imager, all given combinations of gains (1, 2, 3, 5 and 10 eð€€€/ADU) and readout noise values for the three readout speeds (100 kHz, 500 kHz and 1 MHz) are veri ed using the sky ats and bias frames taken during early 2021; measured values resemble well with the theoretical ones. Using colour-colour and colour-magnitude transformation equations, colour coe cients ( ) and zero-points ( ) are determined to constrain and examine their long-term consistencies and any possible evolution based on UBV RI observations of several Landolt standard elds observed during 2016{2021. Our present analysis exhibits consistency among estimated values within the 1 and does not show any noticeable trend with time. We also found that the photometric errors and limiting magnitudes computed using the CCD Imager data followed the earlier simulated ones. The average extinction coe cients, their seasonal variations and zenith night-sky brightness values for the moon-less nights for all ten Bessel UBV RI and SDSS ugriz lters are also estimated and found comparable to those reported for other good astronomical sites. The thesis winds up with a summary of the work done to understand the characteristics of the energetic cosmic transients like SESNe (which includes SLSNe-I, Ib and GRB-SNe) and LGRBs and the correlations between them. Our results clearly demonstrate a possible continuum among these classes of energetic transients in terms of underlying physical mechanisms and environments supporting a common class of possible progenitors. Also, the work presented in this thesis opens up various future prospects to pursue many front line open questions related to stellar evolution and high energy astrophysics that can be addressed using telescopes with larger apertures and high cadences. The results presented in this thesis also highlight that the Imager is a suitable instrument for observing such transients, based on its deep imaging capabilities and the longitudinal advantage of India and especially the 3.6 m DOT site in the near future.