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We report observations of the optical counterpart of the long gamma-ray burst (GRB) GRB 230812B and its associated supernova (SN) SN 2023pel. The proximity ( z = 0.36) and high energy ( E _γ _,iso ∼ 10 ^53 erg) make it an important event to study as a probe of the connection between massive star core collapse and relativistic jet formation. With a phenomenological power-law model for the optical afterglow, we find a late-time flattening consistent with the presence of an associated SN. SN 2023pel has an absolute peak r -band magnitude of M _r = −19.46 ± 0.18 mag (about as bright as SN 1998bw) and evolves on quicker timescales. Using a radioactive heating model, we derive a nickel mass powering the SN of M _Ni = 0.38 ± 0.01 M _⊙ and a peak bolometric luminosity of L _bol ∼ 1.3 × 10 ^43 erg s ^−1 . We confirm SN 2023pel’s classification as a broad-line Type Ic SN with a spectrum taken 15.5 days after its peak in the r band and derive a photospheric expansion velocity of v _ph = 11,300 ± 1600 km s ^−1 at that phase. Extrapolating this velocity to the time of maximum light, we derive the ejecta mass M _ej = 1.0 ± 0.6 M _⊙ and kinetic energy ${E}_{\mathrm{KE}}={1.3}_{-1.2}^{+3.3}\times {10}^{51}\,\mathrm{erg}$ . We find that GRB 230812B/SN 2023pel has SN properties that are mostly consistent with the overall GRB-SN population. The lack of correlations found in the GRB-SN population between SN brightness and E _γ _,iso for their associated GRBs across a broad range of 7 orders of magnitude provides further evidence that the central engine powering the relativistic ejecta is not coupled to the SN powering mechanism in GRB-SN systems.

We present a detailed investigation of photometric, spectroscopic, and polarimetric observations of the Type II SN 2023ixf. Earlier studies have provided compelling evidence for a delayed shock breakout from a confined dense circumstellar matter (CSM) enveloping the progenitor star. The temporal evolution of polarization in the SN 2023ixf phase revealed three distinct peaks in polarization evolution at 1.4 days, 6.4 days, and 79.2 days, indicating an asymmetric dense CSM, an aspherical shock front and clumpiness in the low-density extended CSM, and an aspherical inner ejecta/He-core. SN 2023ixf displayed two dominant axes, one along the CSM-outer ejecta and the other along the inner ejecta/He-core, showcasing the independent origin of asymmetry in the early and late evolution. The argument for an aspherical shock front is further strengthened by the presence of a high-velocity broad absorption feature in the blue wing of the Balmer features in addition to the P-Cygni absorption post-16 days. Hydrodynamical light-curve modeling indicated a progenitor mass of 10 M _⊙ with a radius of 470 R _⊙ and explosion energy of 2 × 10 ^51 erg, along with 0.06 M _⊙ of ^56 Ni, though these properties are not unique due to modeling degeneracies. The modeling also indicated a two-zone CSM: a confined dense CSM extending up to 5 × 10 ^14 cm with a mass-loss rate of 10 ^−2 M _⊙ yr ^−1 and an extended CSM spanning from 5 × 10 ^14 to at least 10 ^16 cm with a mass-loss rate of 10 ^−4 M _⊙ yr ^−1 , both assuming a wind-velocity of 10 km s ^−1 . The early-nebular phase observations display an axisymmetric line profile of [O i ], redward attenuation of the emission of H α post 125 days, and flattening in the Ks -band, marking the onset of dust formation.

We present detailed multiband photometric and spectroscopic observations and analysis of a rare core-collapse supernova, SN 2021wvw, that includes photometric evolution up to 250 days and spectroscopic coverage up to 100 days postexplosion. A unique event that does not fit well within the general trends observed for Type IIP supernovae, SN 2021wvw shows an intermediate luminosity with a short plateau phase of just about 75 days, followed by a very sharp (∼10 days) transition to the tail phase. Even in the velocity space, it lies at a lower velocity compared to a larger Type II sample. The observed peak absolute magnitude is −16.1 mag in r -band, and the nickel mass is well constrained to 0.020 ± 0.006 M _⊙ . Detailed hydrodynamical modeling using MESA+STELLA suggests a radially compact, low-metallicity, high-mass red supergiant progenitor ( M _ZAMS = 18 M _⊙ ), which exploded with ∼0.2 × 10 ^51 erg s ^−1 leaving an ejecta mass of M _ej ≈ 5 M _⊙ . Significant late-time fallback during the shock propagation phase is also seen in progenitor+explosion models consistent with the light-curve properties. As the faintest short-plateau supernova characterized to date, this event adds to the growing diversity of transitional events between the canonical ∼100 days plateau Type IIP and stripped-envelope events.

We report the optical, UV, and soft X-ray observations of the 2017–2022 eruptions of the recurrent nova M31N 2008-12a. We find a cusp feature in the $r^{\prime} $ - and $i^{\prime} $ -band light curves close to the peak, which could be related to jets. The geometry of the nova ejecta based on morpho-kinematic modeling of the H α emission line indicates an extended jet-like bipolar structure. Spectral modeling indicates an ejecta mass of 10 ^−7 –10 ^−8 M _⊙ during each eruption and an enhanced helium abundance. The supersoft source phase shows significant variability, which is anticorrelated to the UV emission, indicating a common origin. The variability could be due to the reformation of the accretion disk. We infer a steady decrease in the accretion rate over the years based on the intereruption recurrence period. A comparison of the accretion rate with different models on the ${M}_{\mathrm{WD}}\mbox{--}\dot{M}$ plane yields the mass of a CO white dwarf, powering the H-shell flashes every ∼1 yr, to be >1.36 M _⊙ and growing with time, making M31N 2008-12a a strong candidate for the single degenerate scenario of the Type Ia supernovae progenitor.

We present early-phase panchromatic photometric and spectroscopic coverage spanning the far-ultraviolet to near-infrared regime of the nearest hydrogen-rich core-collapse supernova (SN) in the last 25 yr, SN 2023ixf. We observe early “flash” features in the optical spectra due to confined dense circumstellar material (CSM). We observe high-ionization absorption lines (Fe ii , Mg ii ) in the ultraviolet spectra from very early on. We also observe a multipeaked emission profile of H α in the spectrum beginning at ∼16 days, which indicates ongoing interaction of the SN ejecta with a preexisting shell-shaped CSM having an inner radius of ∼75 au and an outer radius of ∼140 au. The shell-shaped CSM is likely a result of enhanced mass loss ∼35–65 yr before the explosion assuming a standard red supergiant wind. The UV spectra are dominated by multiple highly ionized narrow absorption and broad emission features from elements such as C, N, O, Si, Fe, and Ni. Based on early light-curve models of Type II SNe, we infer that the nearby dense CSM confined to 7 ± 3 × 10 ^14 cm (∼45 au) is a result of enhanced mass loss (10 ^−3.0±0.5 M _⊙ yr ^−1 ) two decades before the explosion.

We report observations of the optical counterpart of the long gamma-ray burst GRB 221009A. Due to the extreme rarity of being both nearby ( z = 0.151) and highly energetic ( E _γ _,iso ≥ 10 ^54 erg), GRB 221009A offers a unique opportunity to probe the connection between massive star core collapse and relativistic jet formation across a very broad range of γ -ray properties. Adopting a phenomenological power-law model for the afterglow and host galaxy estimates from high-resolution Hubble Space Telescope imaging, we use Bayesian model comparison techniques to determine the likelihood of an associated supernova (SN) contributing excess flux to the optical light curve. Though not conclusive, we find moderate evidence ( K _Bayes = 10 ^1.2 ) for the presence of an additional component arising from an associated SN, SN 2022xiw, and find that it must be substantially fainter (