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We present densely-sampled U BV RI/griz photometric and low-resolution (6-10Å) optical spectroscopic observations from 4 to 270 days after explosion of a newly discovered type II SN 2012aw in a nearby (∼9.9 Mpc) galaxy M95. The light-curve characteristics of apparent magnitudes, colors, bolometric luminosity and the presence and evolution of prominent spectral features are found to have striking similarity with the archetypal IIP SNe 1999em, 1999gi and 2004et. The early time observations of SN 2012aw clearly detect minima in the light-curve of V , R and I bands near 37 days after explosion and this we suggest to be an observational evidence for emergence of recombination phase. The mid-plateau M V magnitude (−16.67 ± 0.04) lies in between the bright (∼ −18) and subluminous (∼ −15) IIP SNe. The mass of nickel is 0.06 ± 0.01 M ⊙ . The SYNOW modelling of spectra indicate that the value and evolution of photospheric velocity is similar to SN 2004et, but about ∼600 km s −1 higher than that of SNe 1999em and 1999gi at comparable epochs. This trend is more apparent in the line velocities of Hα and Hβ. A comparison of ejecta velocity properties with that of existing radiation-hydrodynamical simulations indicate that the energy of explosion lies in the range 1-2×10 51 ergs; a further comparison of nebular phase [O i] doublet luminosity with SNe 2004et and 1987A indicate that the mass of progenitor star is about 14-15 M ⊙ . The presence of high-velocity absorption features in the mid-to-late plateau and possibly in early phase spectra show signs of interaction between ejecta and the circumstellar matter; being consistent with its early-time detection at X-ray and radio wavebands.

We present optical photometric and low-resolution spectroscopic observations of the Type II plateau supernova (SN) 2008in, which occurred in the outskirts of the nearly face-on spiral galaxy M 61. Photometric data in the X-rays, ultraviolet and near-infrared bands have been used to characterize this event. The SN field was imaged with the ROTSE-IIIb optical telescope about seven days before the explosion. This allowed us to constrain the epoch of the shock breakout to JD = 2454825.6. The duration of the plateau phase, as derived from the photometric monitoring, was ∼ 98 days. The spectra of SN 2008in show a striking resemblance to those of the archetypal low-luminosity IIP SNe 1997D and 1999br. A comparison of ejecta kinematics of SN 2008in with the hydrodynamical simulations of Type IIP SNe by Dessart et al. (2010) indicates that it is a less energetic event (∼ 5 × 10 50 erg). However, the light curve indicates that the production of radioactive 56 Ni is significantly higher than that in the low-luminosity SNe. Adopting an interstellar absorption along the SN direction of A V ∼ 0.3 mag and a distance of 13.2 Mpc, we estimated a synthesized 56 Ni mass of ∼ 0.015M ⊙ . Employing semi-analytical formulae (Litvinova & Nadezhin 1985), we derived a pre-SN radius of ∼ 126R ⊙ , an explosion energy of ∼ 5.4 × 10 50 erg and a total ejected mass of ∼ 16.7M ⊙ . The latter indicates that the zero age main-sequence mass of the progenitor did not exceed 20M ⊙ . Considering the above properties of SN 2008in and its occurrence in a region of sub-solar metallicity ([O/H] ∼ 8.44 dex), it is unlikely that fall-back of the ejecta onto a newly formed black hole occurred in SN 2008in. We therefore favor a low-energy explosion scenario of a relatively compact, moderate-mass progenitor star that generates a neutron star.

We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo’s third observing run (O3). We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook follow-up with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization area of 4480 deg2, a median distance of 267 Mpc, and false-alarm rates ranging from 1.5 to 10−25 yr−1. The ZTF coverage in the g and r bands had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. The O3 follow-up by the GROWTH team comprised 340 UltraViolet/Optical/InfraRed (UVOIR) photometric points, 64 OIR spectra, and three radio images using 17 different telescopes. We find no promising kilonovae (radioactivity-powered counterparts), and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. Initially, we assume that all GW triggers are bona fide astrophysical events regardless of false-alarm rate and that kilonovae accompanying BNS and NSBH mergers are drawn from a common population; later, we relax these assumptions. Assuming that all kilonovae are at least as luminous as the discovery magnitude of GW170817 (−16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than −16.6 mag (the extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag day−1 (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations based on the online classifications, the joint probability of zero detections, assuming all kilonovae are brighter than −16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than <57% (<89%) of putative kilonovae could be brighter than −16.6 mag assuming flat evolution (fading by 1 mag day−1) at the 90% confidence level. If we further take into account the online terrestrial probability for each GW trigger, we find that no more than <68% of putative kilonovae could be brighter than −16.6 mag. Comparing to model grids, we find that some kilonovae must have M ej < 0.03 M ⊙, X lan > 10−4, or ϕ > 30° to be consistent with our limits. We look forward to searches in the fourth GW observing run; even 17 neutron star mergers with only 50% coverage to a depth of −16 mag would constrain the maximum fraction of bright kilonovae to <25%.

We present densely-sampled ultraviolet/optical photometric and low-resolution optical spectroscopic observations of the type IIP supernova 2013ab in the nearby (∼24 Mpc) galaxy NGC 5669, from 2 to 190d after explosion. Continuous photometric observations, with the cadence of typically a day to one week, were acquired with the 1-2m class telescopes in the LCOGT network, ARIES telescopes in India and various other telescopes around the globe. The light curve and spectra suggest that the SN is a normal type IIP event with a plateau duration of ∼ 80 days with mid plateau absolute visual magnitude of -16.7, although with a steeper decline during the plateau (0.92 mag 100 d −1 in V band) relative to other archetypal SNe of similar brightness. The velocity profile of SN 2013ab shows striking resemblance with those of SNe 1999em and 2012aw. Following the Rabinak & Waxman (2011) prescription, the initial temperature evolution of the SN emission allows us to estimate the progenitor radius to be ∼ 800 R ⊙ , indicating that the SN originated from a red supergiant star. The distance to the SN host galaxy is estimated to be 24.3 Mpc from expanding photosphere method (epm). From our observations, we estimate that 0.064 M ⊙ of 56 Ni was synthesized in the explosion. General relativistic, radiation hydrodynamical modeling of the SN infers an explosion energy of 0.35 × 10 51 erg, a progenitor mass (at the time of explosion) of ∼ 9 M ⊙ and an initial radius of ∼ 600 R ⊙ .

We present photometric and spectroscopic observations of the type Ibn supernova (SN) 2019uo, the second ever SN Ibn with flash ionization (He II, C III, N III) features in its early spectra. SN 2019uo displays a rapid post-peak luminosity decline of 0.1 mag d −1 similar to most of the SNe Ibn, but is fainter (M V max = −18.30 ± 0.24 mag) than a typical SN Ibn and shows a color evolution that places it between SNe Ib and the most extreme SNe Ibn. SN 2019uo shows P-cygni He I features in the early spectra which gradually evolves and becomes emission dominated post peak. It also shows faster evolution in line velocities as compared to most other members of the type Ibn subclass. The bolometric light curve is fairly described by a 56 Ni + circumstellar interaction model.

We present the low-resolution spectroscopic and UBVRI broad-band photometric investigations of the Type IIb supernova 2011fu, discovered in UGC 01626. The photometric follow-up of this event has been initiated a few days after the explosion and covers a period of about 175 days. The early-phase light curve shows a rise followed by steep decay in all bands and shares properties very similar to that seen in case of SN 1993J, with a possible detection of the adiabatic cooling phase. Modelling of the quasi-bolometric light curve suggests that the progenitor had an extended (∼ 1 × 10 13 cm), low-mass (∼ 0.1 M ⊙ ) H-rich envelope on top of a dense, compact (∼ 2 × 10 11 cm), more massive (∼ 1.1 M ⊙ ) He-rich core. The nickel mass synthesized during the explosion was found to be ∼ 0.21 M ⊙ , slightly larger than seen in case of other Type IIb SNe. The spectral modelling performed with SYNOW suggests that the early-phase line velocities for H and Fe ii features were ∼ 16000 km s −1 and ∼ 14000 km s −1 , respectively. Then the velocities declined up to day +40 and became nearly constant at later epochs.

High cadence ultraviolet, optical and near-infrared photometric and low-resolution spectroscopic observations of the peculiar Type II supernova (SN) 2018hna are presented. The early phase multiband light curves exhibit the adiabatic cooling envelope emission following the shock breakout up to ∼ 14 days from the explosion. SN 2018hna has a rise time of ∼ 88 days in the V -band, similar to SN 1987A. A 56 Ni mass of ∼ 0.087 ± 0.004 M is inferred for SN 2018hna from its bolometric light curve. Hydrodynamical modelling of the cooling phase suggests a progenitor with a radius ∼ 50 R , a mass of ∼ 14-20 M and an explosion energy of ∼ 1.7-2.9× 10 51 erg. The smaller inferred radius of the progenitor than a standard red supergiant is indicative of a blue supergiant progenitor of SN 2018hna. A sub-solar metallicity (∼ 0.3 Z ) is inferred for the host galaxy UGC 07534, concurrent with the low-metallicity environments of 1987A-like events.