Though type-Ia supernovae (SNe Ia) are found in all types of galaxies, recent local Hubble constant measurements have disfavored using SNe Ia in early-type or quiescent galaxies, aiming instead for better consistency with SNe Ia in star-forming, late-type host galaxies calibrated by Cepheid distances. Here we investigate the feasibility of a parallel distance ladder using SNe Ia exclusively in quiescent, massive (log M_*/M_⊙≥ 10) host galaxies, calibrated by tip of the red giant branch (TRGB) distances. We present TRGB measurements to four galaxies: three measured from the Hubble Space Telescope with the ACS F814W filter, and one measured from the JWST NIRCam F090W filter. Combined with literature measurements, we define a TRGB calibrator sample of five high-mass, early-type galaxies that hosted well-measured SNe Ia: NGC 1316 (SN 2006dd), NGC 1380 (SN 1992A), NGC 1404 (SN 2007on, SN 2011iv), NGC 4457 (SN 2020nvb), and NGC 4636 (SN 2020ue). We jointly standardize these calibrators with a fiducial sample of 124 Hubble-flow SNe Ia from the Zwicky Transient Facility that are matched in host-galaxy and light-curve properties. Our results with this homogenized subsample show a Hubble residual scatter of under 0.11 mag, lower than usually observed in cosmological samples of the full SN Ia distribution. We obtain a measurement of the Hubble constant, H_0 = 75.3 ± 2.9 km s^-1 Mpc^-1, including statistical and estimated systematic uncertainties, and discuss the potential to further improve the precision of this approach. As calibrator and supernova samples grow, we advocate that future cosmological applications of SNe Ia use subsamples matched in host-galaxy and supernova properties across redshift.

Hydrogen-rich supernovae (SNe) span a range of hydrogen envelope masses at core collapse, producing diverse light curves from extended plateaus in Type IIP SNe to double-peaked Type IIb SNe (SNe IIb). Recent simulations predict a continuous sequence of light-curve morphologies as hydrogen is removed, with short-plateau (SP; plateau durations ≈50–70 days) SNe emerging as a transitional class. However, the observational boundary between types IIb and SP remains poorly defined, and thus far unobserved. We report on extensive photometric and spectroscopic follow-up of SN 2023wdd and SN 2022acrv, two candidate transitional events on the low-mass end of the SP class. Both exhibit weak, double-peaked light curves, which we interpret as exceptionally short plateaus (10–20 days), and hybrid spectral features: persistent H α absorption with He I contamination, but without the helium dominance characteristic of SNe IIb. Using analytic shock-cooling models and numerical light-curve fitting, we estimate H-rich envelope masses of ∼0.6–0.8 M _⊙ —significantly larger than canonical IIb values (≲0.1 M _⊙ ) but consistent with the ∼0.9 M _⊙ threshold predicted for short-plateau behavior. Although the progenitor radii inferred from analytic and numerical methods differ by factors of 2–5, envelope mass estimates are consistent across approaches. Comparisons to well-studied Type IIb (SN 2016gkg, SN 2022hnt), SP (SN 2023ufx, SN 2006ai, SN 2016egz, SN 2006Y), and Type II (SN 2023ixf, SN 2013ej) SNe suggests a monotonic relationship between hydrogen envelope mass and plateau length, consistent with analytic and numerical expectations. These findings provide additional evidence for a continuous distribution of envelope stripping in H-rich core-collapse progenitors, and place SN 2023wdd and SN 2022acrv along the IIb–SP boundary.

We present optical + near-infrared + mid-infrared (MIR) observations of the normal Type Ia supernovae (SNe Ia) 2022aaiq and 2024gy in the nebular phase, continuously spanning 0.35-28 mu m. Medium-resolution JWST spectroscopy reveals novel narrow (v(FWHM) < 1500 km s(-1)) [Ni ii] 1.94 and 6.64 mu m cores in both events. The MIR [Ni ii] 6.64 mu m line exhibits a distinct narrow core atop a broader base, indicating a central enhancement of stable Ni. This structure points to high central densities consistent with a near-Chandrasekhar-mass (M-Ch) progenitor or a high-metallicity sub-M-Ch progenitor. From detailed line-profile inversions of SN 2024gy, we derive emissivity profiles for stable iron-group elements, radioactive material, and intermediate-mass elements, revealing spatially distinct ejecta zones. The [Ni iii] 7.35 mu m line shows a shallow-to-steep slope transition-a "broken-slope" morphology-that matches predictions for delayed detonation explosions with separated deflagration and detonation ashes. We also reanalyze and compare to archival JWST spectra of SN 2021aefx and the subluminous SN 2022xkq. From the stable Ni luminosities, we infer that SN 2024gy produced similar to 5-10 times more stable Ni mass than SN 2022xkq, favoring a near-M-Ch scenario for SN 2024gy and a sub-M-Ch scenario for SN 2022xkq. These results demonstrate that resolved line profiles, now accessible with JWST, provide powerful diagnostics of explosion geometry, central density, and progenitor mass in SNe Ia.

We present extensive ultraviolet to optical photometric and optical to near-infrared (NIR) spectroscopic follow-up observations of the nearby intermediate-luminosity (MV = -16.81 +/- 0.19 mag) Type Iax supernovae (SNe Iax) 2024pxl in NGC 6384. SN 2024pxl exhibits a faster light curve than the high-luminosity members of this class, and slower than low-luminosity events. The observationally well-constrained rise time of similar to 11 days and an estimated synthesized 56Ni mass of 0.03 M circle dot, based on analytical modeling of the integrated spectral energy distribution light curve, are consistent with models of the weak deflagration of a carbon-oxygen white dwarf. Our optical spectral sequence of SN 2024pxl shows weak Si ii lines and spectral evolution similar to other high-luminosity SNe Iax, but also a prominent early-time C ii line, like lower-luminosity SNe Iax. The late-time optical spectrum of SN 2024pxl closely matches that of SN 2014dt, and its NIR spectral evolution aligns with that of other well-studied, high-luminosity SNe Iax. The spectral-line expansion velocities of SN 2024pxl are at the lower end of the SNe Iax velocity distribution, and the velocity distribution of iron-group elements compared to intermediate-mass elements suggests that the ejecta are mixed on large scales, as expected in pure deflagration models. SN 2024pxl exhibits characteristics intermediate between those of high-luminosity and low-luminosity SNe Iax, further establishing a link across this diverse class.

We present far- and near-ultraviolet (UV) spectra of the type II supernovae (SNe) SN 2023ixf from days 199 to 722 and SN 2024ggi at days 41 and 232. Both SNe show broad, blueshifted, and asymmetric UV emission lines with an initial maximum velocity of ∼9000 km s ^−1 and narrow unresolved emission in C iv λλ 1548.9, 1550.8. We compare the optical and UV emission-line profiles, showing that they evolve from two distinct velocity profiles to a single profile tracing the UV emission. We interpret this as shock power from interaction with circumstellar material coming to dominate over the radioactive-decay power from the inner ejecta. Comparing our observations to radiative transfer models with injected shock power, we find SN 2024ggi is best matched by P _shock,abs = 1 × 10 ^41 erg s ^−1 at day 40; SN 2023ixf at day 300 and SN 2024ggi at day 200 are best matched by P _shock,abs = 1 × 10 ^40 erg s ^−1; and SN 2023ixf at day 600 is best matched by P _shock,abs = 5 × 10 ^39 erg s ^−1 . From these models, we find that the mass-loss rate of both SNe increased just before the explosion. For SN 2023ixf, our mass-loss rates go from 4 × 10 ^−5 M _⊙ yr ^−1 at 600 yr before explosion to 2 × 10 ^−2 M _⊙ yr ^−1 at 15 yr prior to explosion. For SN 2024ggi, we find a mass-loss rate of 9 × 10 ^−5 M _⊙ yr ^−1 at 150 yr before explosion and 1 × 10 ^−3 M _⊙ yr ^−1 at 30 yr before explosion.

We present the photometric and spectroscopic analysis of five Type Ibn supernovae (SNe): SN 2020nxt, SN 2020taz, SN 2021bbv, SN 2023utc, and SN 2024aej. These events share key observational features and belong to a family of objects similar to the prototypical Type Ibn SN 2006jc. The SNe exhibit rise times of approximately 10 days and peak absolute magnitudes ranging from -16.5 to -19 mag. Notably, SN 2023utc is the faintest Type Ibn SN discovered to date, with an exceptionally low r-band absolute magnitude of -16.4 mag. The pseudo-bolometric light curves peak at (1 - 10)x10(42) erg s(-1), with total radiated energies on the order of (1 - 10)x10(48) erg. Spectroscopically, these SNe display a relatively slow spectral evolution. The early spectra are characterised by a hot blue continuum and prominent He I emission lines. The early spectra also show blackbody temperatures exceeding 10 000 K, with a subsequent decline in temperature during later phases. Narrow He I lines, which are indicative of unshocked circumstellar material (CSM), show velocities of approximately 1000 km s(-1). The spectra suggest that the progenitors of these SNe underwent significant mass loss prior to the explosion, resulting in a He-rich CSM. Our light curve modelling yielded estimates for the ejecta mass (M-ej) in the range 1 - 3 M-circle dot with kinetic energies (E-Kin) of (0.1 - 1)x10(50) erg. The inferred CSM mass ranges from 0.2 to 1 M-circle dot. These findings are consistent with expectations for core collapse events arising from relatively massive envelope-stripped progenitors.

Context. Core-collapse supernovae (CCSNe) may have contributed a significant amount of dust in the early Universe. Freshly formed coolant molecules (e.g., CO) and warm dust can be found in CCSNe as early as similar to 100 d after the SN explosion, allowing the study of their evolution with time series observations. Aims. Through study of the Type II SN 2023ixf, we aim to investigate the temporal evolution of the temperature, velocity, and mass of CO and compare them with other CCSNe, exploring their implications for the dust formation in CCSNe. From observations of velocity profiles of lines of other species (e.g., H and He), we also aim to characterize and understand the interaction of the SN ejecta with preexisting circumstellar material (CSM). Methods. We present a time series of 16 near-infrared spectra of SN 2023ixf from 9 to 307 d, taken with multiple instruments: Gemini/GNIRS, Keck/NIRES, IRTF/SpeX, and MMT/MMIRS. Results. The early (t less than or similar to 70 d) spectra indicate interaction between the expanding ejecta and nearby CSM. At t less than or similar to 20 d, intermediate-width line profiles corresponding to the ejecta-wind interaction are superposed on evolving broad P Cygni profiles. We find intermediate-width and narrow lines in the spectra until t less than or similar to 70 d, which suggest continued CSM interaction. We also observe and discuss high-velocity absorption features in H alpha and H beta line profiles formed by CSM interaction. The spectra contain CO first overtone emission between 199 and 307 d after the explosion. We modeled the CO emission and found the CO to have a higher velocity (3000-3500 km s(-1)) than that in Type II-pec SN 1987A (1800-2000 km s(-1)) during similar phases (t = 199 - 307 d) and a comparable CO temperature to SN 1987A. A flattened continuum at wavelengths greater than 1.5 mu m accompanies the CO emission, suggesting that the warm dust is likely formed in the ejecta. The warm dust masses are estimated to be on the order of similar to 10(-5) M-circle dot.

Context. This is the second paper of a series aiming to determine the birth rates of supernovae (SNe) in the local Universe. Aims. We aimed to estimate the SN rates in the local Universe and fit the delay-time distribution of type Ia SNe (SNe Ia) to put constraints on their progenitor scenarios. Methods. We performed a Monte Carlo simulation to estimate volumetric rates using the nearby SN sample introduced in Paper I. The rate evolution of core-collapse (CC) SNe closely follows the evolution of the cosmic star formation history, while the rate evolution of SNe Ia involves the convolution of the cosmic star formation history and a two-component delay-time distribution including a power law and a Gaussian component. Results. The volumetric rates of type Ia, Ibc, and II SNe are derived as 0.325 +/- 0.040(-0.010)(+0.016), 0.160 +/- 0.028(-0.014)(+0.044), and 0.528 +/- 0.051(-0.013)(+0.162) (in units of 10(-4)yr(-1) Mpc(-3) h(70)(3)), respectively. The rate of CCSNe (0.688 +/- 0.078(-0.027)(+0.0206)) is consistent with previous estimates, which trace the star formation history. Conversely, the newly derived local SN Ia rate is larger than existing results given at redshifts 0.01 < z < 0.1, favoring an increased rate from the Universe at z similar to 0.1 to the local Universe at z < 0.01. A two-component model effectively reproduces the rate variation, with the power law component accounting for the rate evolution at larger redshifts and the Gaussian component with a delay time of 12.63 +/- 0.38 Gyr accounting for the local rate evolution. This delayed component, with its exceptionally long delay time, suggests that the progenitors of these SNe Ia were formed around 1 Gyr after the birth of the Universe, which could only be explained by a double-degenerate progenitor scenario. Comparison with the Palomar Transient Factory (PTF) sample of SNe Ia at z = 0.073 and the morphology of their host galaxies, reveals that the increased SN Ia rate at z < 0.01 is primarily due to the SNe Ia of massive E and S0 galaxies with old stellar populations. Based on the above results, we estimate the Galactic SN rate as 3.08 +/- 1.29 per century.

Our understanding of cosmology is shaped by type Ia supernovae (SNe Ia), the runaway thermonuclear detonations of white dwarfs via accretion from a companion star. The nature of this companion star is highly debated, with disparate models explaining the currently available SNe Ia data. Critical ultraviolet (UV) signatures of SNe Ia progenitors are only observable within the first few days post-detonation. We present the instrument design of the Ultraviolet Type Ia (UVIa) Supernova Mission, a proposed SmallSat to make early UV observations of SNe Ia. UVIa conducts simultaneous observations in three photometric channels: far-UV (1500 to 1800 angstrom), near-UV (1800 to 2400 angstrom), and Sloan u-band (3000 to 4200 angstrom). UVIa employs two 80-mm double-offset Cassegrain UV telescopes and a similar 50-mm u-band telescope, imaging onto three Teledyne e2v CIS120-10-LN complementary metal-oxide semiconductor (CMOS) detectors. The UV detectors are delta-doped for enhanced sensitivity, with custom metal-dielectric filters providing further in-band efficiency and red light rejection. The UV optics utilize multi-layer coatings, defining the UV bandpasses and providing additional red light rejection. The instrument design achieves high UV sensitivity (21.5 mag AB) and superior red light rejection (<10(-5) throughput), allowing UVIa to make early observations of SNe Ia while serving as a pathfinder for future UV transient telescopes.

While the subclass of interacting supernovae (SNe) with narrow hydrogen emission lines (Type IIn supernovae (SNe IIn)) consists of some of the longest-lasting and brightest supernovae (SNe) ever discovered, their progenitors are still not well understood. Investigating SNe IIn as they emit across the electromagnetic spectrum is the most robust way to understand the progenitor evolution before the explosion. This work presents X-ray, optical, infrared, and radio observations of the strongly interacting Type IIn supernova, SN 2020ywx, covering a period >1200 days after discovery. Through multiwavelength modeling, we find that the progenitor of 2020ywx was losing mass at ∼10 ^−2 –10 ^−3 M _⊙ yr ^−1 for at least 100 yr pre-explosion using the circumstellar medium (CSM) speed of 120 km s ^−1 measured from optical and near-infrared (NIR) spectra. Despite the similar magnitude of mass loss measured in different wavelength ranges, we find discrepancies between the X-ray and optical/radio-derived mass-loss evolution, which suggest asymmetries in the CSM. Furthermore, we find evidence for dust formation due to the combination of a growing blueshift in optical emission lines and NIR continuum emission which we fit with blackbodies at ∼1000 K. Based on the observed elevated mass loss over more than 100 yr and the configuration of the CSM inferred from the multiwavelength observations, we invoke binary interaction as the most plausible mechanism to explain the overall mass-loss evolution. SN 2020ywx is thus a case that may support the growing observational consensus that SNe IIn mass loss is explained by binary interaction.

The Ultraviolet (UV) Type Ia Supernova CubeSat (UVIa) is a CubeSat/SmallSat mission concept that stands to test critical space-borne UV technology for future missions like the Habitable Worlds Observatory (HWO) while elucidating long-standing questions about the explosion mechanisms of Type Ia supernovae (SNe Ia). UVIa will observe whether any SNe Ia emit excess UV light shortly after explosion to test progenitor/explosion models and provide follow-up over many days to characterize their UV and optical flux variations over time, assembling a comprehensive multi-band UV and optical low-redshift anchor sample for upcoming high-redshift SNe Ia surveys (e.g., Euclid, Vera Rubin Observatory, Nancy Roman Space Telescope). UVIa's mission profile requires it to perform rapid and frequent visits to newly discovered SNe Ia, simultaneously observing each SNe Ia in two UV bands (FUV: 1500-1800A and NUV: 1800-2400A) and one optical band (u-band: 3000-4200A). In this study, we describe the UVIa mission concept science motivation, mission design, and key technology development.

We present extensive optical observations of a nearby Type Ia supernova (SN Ia), SN 2021hpr, located in the spiral galaxy NGC 3147 at a distance of $\sim$ 45 Mpc. Our observations cover a phase within $\sim 1-2$ days to $\sim 290$ days after the explosion. SN 2021hpr is found to be a spectroscopically normal SN Ia, with an absolute B-band peak magnitude of $M_{max}(B) \approx -19.16 \pm 0.14$ mag and a post-peak decline rate of $\Delta m_{15}(B)= 1.00 \pm 0.01 $ mag. Early-time light curves showed a $\sim 7.0 \%$ excess emission compared to a homogeneously expanding fireball model, likely due to SN ejecta interacting with a companion or immediate circumstellar matter. The optical spectra of SN 2021hpr are overall similar to those of normal SNe Ia, but characterized by prominent detached high-velocity features (HVFs) of Si {\sc ii} and Ca {\sc ii} in the early phase. After examining a small sample of well-observed normal SNe Ia, we find that the HVFs are likely common for the subgroup with early-excess emission. The association of early bump feature with the HVFs could be attributed to density or abundance enhancement at the outer layer of the exploding star, likely as a result of interactions with companion$/$CSM or experiencing more complete burning. Nevertheless, the redshifted Fe {\sc ii} and Ni {\sc ii} lines in the nebular-phase spectra of SN 2021hpr, contrary to the blueshift trend seen in other SNe Ia showing early bump features, indicate its peculiarity in the explosion that remains to be understood.

We present the long-term photometric and spectroscopic analysis of a transitioning SN IIn/Ibn from -10.8 d to 150.7 d post V-band maximum. SN 2021foa shows prominent He i lines comparable in strength to the H alpha line around peak, placing SN 2021foa between the SN IIn and SN Ibn populations. The spectral comparison shows that it resembles the SN IIn population at pre-maximum, becomes intermediate between SNe IIn/Ibn, and at post-maximum matches with SN IIn 1996al. The photometric evolution shows a precursor at -50 d and a light curve shoulder around 17 d. The peak luminosity and colour evolution of SN 2021foa are consistent with most SNe IIn and Ibn in our comparison sample. SN 2021foa shows the unique case of an SN IIn where the narrow P-Cygni in H alpha becomes prominent at 7.2 d. The H alpha profile consists of a narrow (500-1200 km s(-1)) component, intermediate width (3000-8000 km s(-1)) and broad component in absorption. Temporal evolution of the H alpha profile favours a disc-like CSM geometry. Hydrodynamical modelling of the light curve well reproduces a two-component CSM structure with different densities (rho proportional to r(-2)-rho proportional to r(-5)), mass-loss rates (10(-3)-10(-1) M-circle dot yr(-1)) assuming a wind velocity of 1000 km s(-1) and having a CSM mass of 0.18 M-circle dot. The overall evolution indicates that SN 2021foa most likely originated from an LBV star transitioning to a WR star with the mass-loss rate increasing in the period from 5 to 0.5 yr before the explosion or it could be due to a binary interaction.

We present optical photometry and spectroscopy of SN 2019hnl. Discovered within ∼26 hr of explosion by the ATLAS survey, SN 2019hnl is a typical Type IIP supernova (SN) with a peak absolute V -band magnitude of −16.7 ± 0.1 mag, a plateau length of ∼107 days, and an early decline rate of 0.0086 ± 0.0006 mag (50 days) ^−1 . We use nebular spectroscopy and hydrodynamic modeling with the snec , mesa , and stella codes to infer that the progenitor of SN 2019hnl was an M _ZAMS ∼ 11 M _⊙ red supergiant, which produced 0.047 ± 0.007 M _⊙ of ^56 Ni in the explosion. As a part of our hydrodynamic modeling, we reduced hydrogen envelope mass by scaling the mass loss within the “Dutch” wind scheme to fit our light curve, showing that the progenitor of a relatively typical Type IIP SN may experience partial stripping during their evolution and establish massive (∼0.2 M _⊙ ) circumstellar material environments prior to core collapse.

We present extensive optical observations of a nearby Type Ia supernova (SN Ia), SN 2021hpr, located in the spiral galaxy NGC 3147 at a distance of ∼45 Mpc. Our observations cover a phase within ∼1–2 days to ∼290 days after the explosion. SN 2021hpr is found to be a spectroscopically normal SN Ia, with an absolute B -band peak magnitude of M max ( B ) ≈ − 19.16 ± 0.14 mag and a postpeak decline rate of Δ m 15 ( B ) = 1.0 ± 0.01 mag. Early time light curves showed a ∼7.0% excess emission compared to a homogeneously expanding fireball model, likely due to SN ejecta interacting with a companion or immediate circumstellar matter (CSM). The optical spectra of SN 2021hpr are overall similar to those of normal SNe Ia, but characterized by prominent detached high-velocity features (HVFs) of Si ii and Ca ii in the early phase. After examining a small sample of well-observed normal SNe Ia, we find that the HVFs are likely common for the subgroup with early excess emission. The association of an early bump feature with the HVFs could be attributed to density or abundance enhancement at the outer layer of the exploding star, likely as a result of interactions with companion/CSM or experiencing more complete burning. Nevertheless, the redshifted Fe ii and Ni ii lines in the nebular-phase spectra of SN 2021hpr, contrary to the blueshift trend seen in other SNe Ia showing early bump features, indicate its peculiarity in the explosion that remains to be understood.

We present panchromatic optical + near-infrared (NIR) + mid-infrared (MIR) observations of the intermediate-luminosity Type Iax supernova (SN Iax) 2024pxl and the extremely low-luminosity SN Iax 2024vjm. JWST observations provide unprecedented MIR spectroscopy of SN Iax, spanning from +11 to +42 day past maximum light. We detect forbidden emission lines in the MIR at these early times while the optical and NIR are dominated by permitted lines with an absorption component. Panchromatic spectra at early times can thus simultaneously show nebular and photospheric lines, probing both inner and outer layers of the ejecta. We identify spectral lines not seen before in SN Iax, including [Mg ii ] 4.76 μ m, [Mg ii ] 9.71 μ m, [Ne ii ] 12.81 μ m, and isolated O i 2.76 μ m that traces unburned material. Forbidden emission lines of all species are centrally peaked with similar kinematic distributions, indicating that the ejecta are well mixed in both SN 2024pxl and SN 2024vjm, a hallmark of pure deflagration explosion models. Radiative transfer modeling of SN 2024pxl shows good agreement with a weak deflagration of a near-Chandrasekhar-mass white dwarf, but additional IR flux is needed to match the observations, potentially attributable to a surviving remnant. Similarly, we find SN 2024vjm is also best explained by a weak deflagration model, despite the large difference in luminosity between the two supernovae. Future modeling should push to even weaker explosions and include the contribution of a bound remnant. Our observations demonstrate the diagnostic power of panchromatic spectroscopy for unveiling explosion physics in thermonuclear supernovae.

We present high-cadence photometric and low-resolution (R similar to 400-700) optical spectroscopic observations of Type IIP supernova, SN 2018pq, which exploded on the outskirts of the galaxy IC 3896A. The optically thick phase ('plateau') lasts approximately 97 d, the plateau duration of normal Type IIP supernovae. SN 2018pq has a V-band absolute magnitude of -16.42 +/- 0.01 mag at 50 d, resembles normal-luminous supernova, and the V-band decline rate of 0.42 +/- 0.06 mag 50 d(-1) during the plateau phase. A steeper decline rate of 11.87 +/- 1.68 mag 100 d(-1) was observed compared to that of typical Type IIP supernovae during the transition between plateau to nebular phase. We employ detailed radiative transfer spectra modelling, tardis, to reveal the photospheric temperature and velocity at two spectral epochs. The well-fitted model spectra indicate SN 2018pq is a spectroscopically normal Type IIP supernova. Semi-analytical light curve modelling suggests the progenitor as a red supergiant star with an ejecta mass of similar to 11 M-circle dot and an initial radius of 424 R-circle dot. On the contrary, hydrodynamical modelling suggests a higher mass progenitor between 14 and 16 M-circle dot.

We present and analyze the extensive optical broadband photometry of the Type II SN 2023ixf up to 1 yr after explosion. We find that, when compared to two preexisting model grids, the bolometric light curve is consistent with drastically different combinations of progenitor and explosion properties. This may be an effect of known degeneracies in Type IIP light-curve models. We independently compute a large grid of MESA+STELLA single-star progenitor and light-curve models with various zero-age main-sequence masses, mass-loss efficiencies, and convective efficiencies. Using the observed progenitor variability as an additional constraint, we select stellar models consistent with the pulsation period and explode them according to previously established scaling laws to match plateau properties. Our hydrodynamic modeling indicates that SN 2023ixf is most consistent with a moderate-energy ( Eexp approximate to 7x1050 erg) explosion of an initially high-mass red supergiant progenitor (greater than or similar to 16.5 M circle dot) that lost a significant amount of mass in its prior evolution, leaving a low-mass hydrogen envelope (less than or similar to 3 M circle dot) at the time of explosion, with a radius greater than or similar to 950 R circle dot and a synthesized 56Ni mass of approximate to 0.068 M circle dot. We posit that previous mass transfer in a binary system may have stripped the envelope of SN 2023ixf's progenitor. The analysis method with pulsation period presented in this work offers a way to break degeneracies in light-curve modeling in the future, particularly with the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time, when a record of progenitor variability will be more common.

We report the results of a rapid follow-up campaign on the Type IIb Supernova (SN) 2022hnt. We present a daily, multi-band, photometric follow-up using the Las Cumbres Observatory, the Zwicky Transient Facility, the orbiting \textit{Swift} observatory, and the Asteroid Terrestrial-impact Last Alert System (ATLAS). A distinctive feature in the light curve of SN 2022hnt and other IIb SNe is an early narrow peak prior to the ${}^{56}$Ni peak caused by rapid shock cooling of the hydrogen envelope, which can serve as an important probe of the properties of the massive progenitor star in the moments before explosion. Using SN 2022hnt as a case study, we demonstrate a framework of considerations for the application of shock cooling models to type IIb SNe, outlining a consistent procedure for future surveys of Type IIb SNe progenitor and explosion properties. \hll{We fit several recent models of shock-cooling emission and obtain progenitor radii between $\sim50$ and $\sim100$ $R_\odot$, as well as hydrogen-enriched envelope masses between $\sim0.01$ and $\sim0.1$ $M_\odot$, both consistent with values for other IIb SNe. One of these models is the model of \cite{Morag2023}, marking the first time this model has been applied to a Type IIb SN.} We evaluate contrasting predictions between shock-cooling models to construct a fiducial parameter set which can be used for comparison to other SNe. Finally, we investigate the possibility of extended wind breakout or precursor emission captured in the earliest detections.

Massive stars end their lives as core-collapse supernovae, among which some extremes are broad-lined type Ic supernovae from Wolf-Rayet stars associated with long-duration gamma-ray bursts (LGRBs) with powerful relativistic jets. Their less-extreme brethren make unsuccessful jets that are choked inside the stars, appearing as X-ray flashes or low-luminosity GRBs. However, there exists a population of extragalactic fast X-ray transients with timescales ranging from seconds to thousands of seconds, whose origins remain obscure. Here we report the discovery of the bright X-ray transient EP240414a detected by the Einstein Probe, which is associated with the type Ic supernova SN 2024gsa at a redshift of 0.401. The X-ray emission evolution is characterized by a very soft energy spectrum peaking at <1.3 keV, which makes it different from known LGRBs, X-ray flashes or low-luminosity GRBs. Follow-up observations at optical and radio bands revealed the existence of a weak relativistic jet that interacts with an extended shell surrounding the progenitor star. Located on the outskirts of a massive galaxy, this event reveals a population of explosions of Wolf-Rayet stars characterized by a less powerful engine that drives a successful but weak jet, possibly owing to a progenitor star with a smaller core angular momentum than in traditional LGRB progenitors.