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Newly installed 3.6m DOT at Nainital (Uttarakhand) is a novel facility for the time domain astronomy. Because of the longitudinal advantage of India, it could be used to study new transients reported by a global network of robotic telescopes. Observations with the 4K × 4K CCD Imager at the axial port of the 3.6m DOT will be very helpful in the near future towards understanding the different physical aspects of time-critical events, e.g., Gamma-ray bursts (GRBs), Supernovae, Gravitational wave candidates, etc. Using the Imager with broadband filters (Bessel UBVRI and SDSS ugriz), ~6.5' × 6.5' images could be obtained to attempt various science goals in synergy with other multi-band facilities. In this study, we present an analysis of unpublished R-band data of GRB 171205A/SN 2017iuk spanning between ~12 to 105 days since burst, that observed using the 3.6m DOT with 4K × 4K CCD Imager. In the R-band light curve, a bump appears to start from ~3 days, which shows the peak at ~15 days after the burst, clearly indicates photometric evidence of association of SN with GRB 171205A.

We explore the study of energetic transients including core-collapse supernovae using various publicly available analysis tools like MESA & SNEC, MOSFiT and SNCOSMO. We used MESA to evolve a star having zero age main sequence mass (Mzams) of 24 M⊙ until the onset of core-collapse. Then we exploded this model using openly available explosion codes, STELLA & SNEC and obatined various observable parameters such as bolometric luminosity and photospheric velocities etc. We also used MOSFiT to model the light curve of a type Ic supernova, SN1999ex and obtained various physical parameters. SNCOSMO is used for template fitting of various supernovae by varying various parameters such as red shift, dust map, stretch factor of light curve, explosion epoch of supernova etc.

TeV emissions from γ-ray bursts are very important to study their origin and the radiation mechanisms in detail. Recent observations of TeV photons in some of the GRBs are challenging to be explained by the traditional Synchrotron radiation mechanism. In this work, we present the results of a detailed investigation of the prompt and afterglow emissions of recently discovered TeV GRBs (GRB 180720B, GRB 190114C, and GRB 190829A) based on the publicly available prompt and afterglow data including 10.4m GTC and 1.3m DFOT telescopes observations of the first HESS and MAGIC bursts, respectively. Timeresolved spectroscopy of prompt emission of GRB 180720B and GRB 190114C shows an intensity tracking nature of peak energy. In the case of GRB 190829A, peak energy evolution shows a hard to soft tracking trend followed by a very soft and chaotic trend. GRB 190829A is a peculiar intermediate luminous two episodic burst with first emission episode outlier to Amati correlation. We analyzed the late time Fermi-LAT emission that encapsulates the H.E.S.S. and MAGIC observations. Some of the LAT photons are likely to be associated with these GRBs and they could have an Inverse Compton radiation mechanism.