Optical, near-infrared (NIR) photometric and spectroscopic studies, along with the optical imaging polarimetric results for SN 2012au, are presented in this article to constrain the nature of the progenitor and other properties. Well-calibrated multi
band optical photometric data (from $-$0.2 to +413 d since $B$-band maximum) were used to compute the bolometric light curve and to perform semi-analytical light-curve modelling using the $texttt{MINIM}$ code. A spin-down millisecond magnetar-powered model explains the observed photometric evolution of SN 2012au reasonably. Early-time imaging polarimetric follow-up observations ($-$2 to +31 d) and comparison with other similar cases indicate signatures of asphericity in the ejecta. Good spectral coverage of SN 2012au (from $-$5 to +391 d) allows us to trace the evolution of layers of SN ejecta in detail. SN 2012au exhibits higher line velocities in comparison with other SNe Ib. Late nebular phase spectra of SN 2012au indicate a Wolf$-$Rayet star as the possible progenitor for SN 2012au, with oxygen, He-core, and main-sequence masses of $sim$1.62 $pm$ 0.15 M$_odot$, $sim$4$-$8 M$_odot$, and $sim$17$-$25 M$_odot$, respectively. There is a clear absence of a first overtone of carbon monoxide (CO) features up to +319 d in the $K$-band region of the NIR spectra. Overall analysis suggests that SN 2012au is one of the most luminous slow-decaying Type Ib SNe, having comparatively higher ejecta mass ($sim$4.7$-$8.3 M$_odot$) and kinetic energy ($sim$[4.8 $-$ 5.4] $times$ 10$^{51}$ erg). Detailed modelling using $texttt{MESA}$ and the results obtained through $texttt{STELLA}$ and $texttt{SNEC}$ explosions also strongly support spin-down of a magnetar with mass of around 20 M$_odot$ and metallicity Z = 0.04 as a possible powering source of SN 2012au.
We present and perform a detailed analysis of multi-wavelength observations of thisgrb, an optical bright GRB with an observed reverse shock (RS) signature. Observations of this GRB were acquired with the BOOTES-4 robotic telescope, the fermi, and th
e swift missions. Time-resolved spectroscopy of the prompt emission shows that changes to the peak energy (Ep) tracks intensity and the low-energy spectral index seems to follow the intensity for the first episode, whereas this tracking behavior is less clear during the second episode. The fit to the afterglow light curves shows that the early optical afterglow can be described with RS emission and is consistent with the thin shell scenario of the constant ambient medium. The late time afterglow decay is also consistent with the prediction of the external forward shock (FS) model. We determine the properties of the shocks, Lorentz factor, magnetization parameters, and ambient density of thisgrb, and compare these parameters with another 12 GRBs, consistent with having RS produced by thin shells in an ISM-like medium. The value of the magnetization parameter ($R_{rm B} approx 18$) indicates a moderately magnetized baryonic dominant jet composition for thisgrb. We also report the host galaxy photometric observations of thisgrb obtained with 10.4m GTC, 3.5m CAHA, and 3.6m DOT telescopes and find the host (photo $z$ = $2.8^{+0.7}_{-0.9}$) to be a high mass, star-forming galaxy with a star formation rate of $20 pm 10 msun$ $rm yr^{-1}$.
Photometric and spectroscopic analyses of the intermediate-luminosity Type Ib supernova (SN) 2015ap and of the heavily reddened Type Ib SN~2016bau are discussed. Photometric properties of the two SNe, such as colour evolution, bolometric luminosity,
photospheric radius, temperature, and velocity evolution, are also constrained. The ejecta mass, synthesised nickel mass, and kinetic energy of the ejecta are calculated from their light-curve analysis. We also model and compare the spectra of SN~2015ap and SN~2016bau at various stages of their evolution. The P~Cygni profiles of various lines present in the spectra are used to determine the velocity evolution of the ejecta. To account for the observed photometric and spectroscopic properties of the two SNe, we have computed 12,$M_odot$ zero-age main sequence (ZAMS) star models and evolved them until the onset of core collapse using the publicly available stellar-evolution code {tt MESA}. Synthetic explosions were produced using the public version of {tt STELLA} and another publicly available code, {tt SNEC}, utilising the {tt MESA} models. {tt SNEC} and {tt STELLA} provide various observable properties such as the bolometric luminosity and velocity evolution. The parameters produced by {tt SNEC}/{tt STELLA} and our observations show close agreement with each other, thus supporting a 12,$M_odot$ ZAMS star as the possible progenitor for SN~2015ap, while the progenitor of SN~2016bau is slightly less massive, being close to the boundary between SN and non-SN as the final product.
We investigate the observational properties of a hydrogen-deficient superluminous supernova (SLSN) SN 2020ank (at z = 0.2485), with the help of early phase observations carried out between $-$21 and +52 d since $g$-band maximum. Photometrically, SN 2
020ank is one of the brightest SLSN ($M_{g,peak}$ $sim$ $-$21.84 $pm$ 0.10 mag), having fast pre-peak rising and post-peak decaying rates. The bolometric light curve of SN 2020ank exhibits a higher peak luminosity ($L_{max}$) of $sim$(3.9 $pm$ 0.7) $times$ 10$^{44}$ erg s$^{-1}$ and appears to be symmetric around the peak with $L^{rise}_{max}$/e $approx$ $L^{fall}_{max}$/e $approx$ 15 d. The semi-analytical light-curve modelling using the MINIM code suggests a spin down millisecond magnetar with $P_i$ $sim$2.2 $pm$ 0.5 ms and $B$ $sim$(2.9 $pm$ 0.1) $times$ $10^{14}$ G as a possible powering source for SN 2020ank. The possible magnetar origin and excess ultraviolet flux at early epochs indicate a central-engine based powering source for SN 2020ank. Near-peak spectra of SN 2020ank are enriched with the W-shaped O II features but with the weaker signatures of C II and Fe III. Using the estimated rise time of $sim$27.9 d and the photospheric velocity of $sim$12050 km s$^{-1}$, we constrain the ejecta mass to $sim$7.2 $M_{odot}$ and the kinetic energy of $sim$6.3 $times$ 10$^{51}$ erg. The near-peak spectrum of SN 2020ank exhibits a close spectral resemblance with that of fast-evolving SN 2010gx. The absorption features of SN 2020ank are blueshifted compared to Gaia16apd, suggesting a higher expansion velocity. The spectral similarity with SN 2010gx and comparatively faster spectral evolution than PTF12dam (a slow-evolving SLSN) indicate the fast-evolving behavior of SN 2020ank.
We investigate the prompt emission and the afterglow properties of short duration gamma-ray burst (sGRB) 130603B and another eight sGRB events during 2012-2015, observed by several multi-wavelength facilities including the GTC 10.4m telescope. Prompt
emission high energy data of the events were obtained by INTEGRAL/SPI/ACS, Swift/BAT and Fermi/GBM satellites. The prompt emission data by INTEGRAL in the energy range of 0.1-10 MeV for sGRB 130603B, sGRB 140606A, sGRB 140930B, sGRB 141212A and sGRB 151228A do not show any signature of the extended emission or precursor activity and their spectral and temporal properties are similar to those seen in case of other short bursts. For sGRB130603B, our new afterglow photometric data constraints the pre jet-break temporal decay due to denser temporal coverage. For sGRB 130603B, the afterglow light curve, containing both our new as well as previously published photometric data is broadly consistent with the ISM afterglow model. Modeling of the host galaxies of sGRB 130603B and sGRB 141212A using the LePHARE software supports a scenario in which the environment of the burst is undergoing moderate star formation activity. From the inclusion of our late-time data for 8 other sGRBs we are able to; place tight constraints on the non-detection of the afterglow, host galaxy or any underlying kilonova emission. Our late-time afterglow observations of the sGRB 170817A/GW170817 are also discussed and compared with the sub-set of sGRBs.
The upcoming 4-m International Liquid Mirror Telescope (ILMT) facility will perform deep imaging (in single scan $g$ $sim$22 mag.) of a narrow strip of sky each clear night in the Time Delayed Integration mode. A cadence of one day observation will p
rovide unique opportunities to discover different types of supernovae (SNe) along with many other types of variable sources. We present the approach to discover SNe with the ILMT and discuss the follow-up strategy in the context of other existing observational facilities. The advantages of the ILMT observations over the traditional glass mirror telescopes are also discussed.
As an in-house instrument developmental activity at ARIES, the 4Kx4K CCD Imager is designed and developed as a first-light instrument for the axial port of the 3.6m DOT. The f/9 beam of the telescope having a plate-scale of ~ 6.4 arc-sec/mm is utiliz
ed to conduct deeper photometry within the central 10 arc-min field of view. The pixel size of the blue-enhanced liquid Nitrogen cooled STA4150 4Kx4K CCD chip is 15 micron, with options to select gain and speed values to utilize the dynamic range. Using the Imager, it is planned to image the central ~ 6.5x6.5 arc-min^2 field of view of the telescope for various science goals by getting deeper images in several broad-band filters for point sources and objects with low surface brightness. The fully assembled Imager along with automated filter wheels having Bessel UBVRI and SDSS ugriz filters was tested in late 2015 at the axial port of the 3.6m DOT. This instrument was finally mounted at the axial port of the 3.6m DOT on 30th March 2016 when the telescope was technically activated jointly by the Prime Ministers of India and Belgium. This instrument is expected to serve as a general purpose multi-band deep imaging instrument for variety of science goals including studies of cosmic transients, active galaxies, star clusters and optical monitoring of X-ray sources discovered by the newly launched Indian space-mission called ASTROSAT and follow-up of radio bright objects discovered by the GMRT.
We present results based on follow-up observations of the Type II-plateau supernova (SN) 2013ej at 6 epochs spanning a total duration of $sim$37 d. The $R_{c}$-band linear polarimetric observations were carried out between the end of the plateau and
the beginning of the nebular phases as noticed in the photometric light curve. The contribution due to interstellar polarization (ISP) was constrained by using couple of approaches, i.e. based upon the observations of foreground stars lying within 5arcmin, and 10$degr$ radius of the SN location and also investigating the extinction due to the Milky Way and host galaxy towards the SN direction. Our analysis revealed that in general the intrinsic polarization of the SN is higher than the polarization values for the foreground stars and exhibits an increasing trend during our observations. After correcting the ISP of $sim$0.6 per cent, the maximum intrinsic polarization of SN~2013ej is found to be 2.14 $pm$ 0.57 per cent. Such a strong polarization has rarely been seen in Type II-P SNe. If this is the case, i.e., the `polarization bias effect is still negligible, the polarization could be attributed to the asymmetry of the inner ejecta of the SN because the ISP towards the SN location is estimated to be, at most, 0.6 per cent.
From the launch of the Fermi Gamma-ray Space Telescope to July 9, 2010, the Gamma-ray Burst Monitor (GBM) has detected 497 probable GRB events. Twenty-two of these satisfy the simultaneous requirements of an estimated burst direction within 52^circ o
f the Fermi Large Area Telescope (LAT) boresight and a low energy fluence exceeding 5 $mu$erg/cm^2. Using matched filter techniques, the spatially correlated Fermi/LAT photon data above 100 MeV have been examined for evidence of bursts that have so far evaded detection at these energies. High energy emission is detected with great confidence for one event, GRB 090228A. Since the LAT has significantly better angular resolution than the GBM, real-time application of these methods could open the door to optical identification and richer characterization of a larger fraction of the relatively rare GRBs that include high energy emission.
Since the launch of the Fermi Gamma-ray Space Telescope on June 11, 2008, 55 gamma-ray bursts (GRBs) have been observed at coordinates that fall within 66^circ of the Fermi Large Area Telescope (LAT) boresight with precise localizations provided by t
he NASA Swift mission or other satellites. Imposing selection cuts to exclude low Galactic latitudes and high zenith angles reduces the sample size to 41. Using matched filter techniques, the Fermi/LAT photon data for these fields have been examined for evidence of bursts that have so far evaded detection at energies above 100 MeV. Following comparisons with similar random background fields, two events, GRB 080905A and GRB 091208B, stand out as excellent candidates for such an identification. After excluding the six bright bursts previously reported by the LAT team, the remaining 35 events exhibit an excess of LAT diffuse photons with a statistical significance greater than 2 sigma, independent of the matched filter analysis. After accounting for the total number of photons in the well-localized fields and including estimates of detection efficiency, one concludes that somewhere in the range of 11% to 19% of all GRBs within the LAT field of view illuminate the detector with two or more energetic photons. These are the most stringent estimates of the high energy photon content of GRBs to date. The two new events associated with high energy photon emission have similar ratios of high to low energy fluences as observed previously. This separates them from bursts with similar low energy fluences by a factor of ten, suggesting a distinct class of events rather than a smooth continuum.
