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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.

We present the poster titled 'Probing into emission mechanisms of \thisgrb using time-resolved spectra and polarization studies: Synchrotron Origin? In thiswork, we haveexplored different aspects of the prompt emission and afterglow of multi-pulsed GRB 190530A(the sixth most fluent GBM burst detected so far) detected by the GBM and LAT and compared them with similar bursts. This poster presents the timing, spectral, and polarimetric analysis of the prompt emission observed using AstroSat and Fermi to provide insight into the prompt emission radiation mechanisms.Furthermore, we also report the earliest optical observations constraining afterglow polarization using the MASTER and the redshift measurement (z= 0.9386) obtained with the 10.4m GTC telescopes, making the burst the first case where both prompt emission and afterglow polarization measurements are constrained.&nbsp

In this work, we study the synthetic explosions of a massive star. We take a 100 M$_{\odot}$ zero--age main--sequence (ZAMS) star and evolve it until the onset of core-collapse using {\tt MESA}. Then, the resulting star model is exploded using the publicly available stellar explosion code, {\tt STELLA}. The outputs of {\tt STELLA} calculations provide us the bolometric light curve and photospheric velocity evolution along with other physical properties of the underlying supernova. In this paper, the effects of having large Hydrogen-envelope on the supernova light curve have been explored. We also explore the effects of the presence of different amounts of nickel mass and the effect of changing the explosion energy of the resulting supernovae from such heavy progenitors, on their bolometric light curves and photospheric velocities., Comment: Published as a Special Issue of Journal of Astrophysics and Astronomy, 2022, Astrophysical jets and observational facilities: National perspective, 05 -09 April 2021, ARIES Nainital

In this paper, we present multi-band photometric observations and analysis of the host galaxies for a sample of five interesting gamma-ray bursts (GRBs) observed using the 3.6m Devasthal optical telescope (DOT) and the back-end instruments. The host galaxy observations of GRBs provide unique opportunities to estimate the stellar mass, ages, star-formation rates and other vital properties of the burst environments and hence, progenitors. We performed a detailed spectral energy distribution (SED) modeling of the five host galaxies using an advanced tool called Prospector, a stellar population synthesis model. Furthermore, we compared the results with a larger sample of well-studied host galaxies of GRBs, supernovae and normal star-forming galaxies. Our SED modeling suggests that GRB 130603B, GRB 140102A, GRB 190829A and GRB 200826A have massive host galaxies with high star-formation rates (SFRs). On the other hand, a supernovae-connected GRB 030329 has a rare low-mass galaxy with a low star-formation rate. We also find that GRB 190829A has the highest (in our sample) amount of visual dust extinction and gas in its local environment of the host, suggesting that the observed very high-energy emission from this burst might have a unique local environment. Broadly, the five GRBs in our sample satisfy the typical correlations between host galaxies parameters and these physical parameters are more common to normal star-forming galaxies at the high-redshift Universe. Our results also demonstrate the capabilities of 3.6m DOT and the back-end instruments for the deeper photometric studies of the host galaxies of energetic transients, such as GRBs, supernovae and other transients in the long run. © Indian Academy of Sciences., RG, and SBP acknowledge BRICS grant DST/IMRCD/BRICS/PilotCall1/ProFCheap/2017(G) for the financial support. RG and SBP acknowledge the financial support of ISRO under AstroSat archival Data utilization program (DS_2B-13013(2)/1/2021-Sec.2). AA acknowledges funds and assistance provided by the Council of Scientific & Industrial Research (CSIR), India, with file no. 09/948(0003)/2020-EMR-I. AJCT and SBP acknowledge support from the Spanish ministry project PID2020-118491GB-I00. AJCT also acknowledges Junta de Andalucía project P20_01068 and the ‘Center of Excellence Severo Ochoa’ award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). This research is based on the observations obtained at the 3.6m Devasthal optical telescope (DOT), which is a national facility run and managed by Aryabhatta Research Institute of Observational Sciences (ARIES), an autonomous Institute under Department of Science and Technology, Government of India.