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Abstract 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 absoluteV-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 thesnec,mesa, andstellacodes to infer that the progenitor of SN 2019hnl was anM_ZAMS ∼ 11M_⊙red supergiant, which produced 0.047 ± 0.007M_⊙of⁵⁶Ni 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 (∼0.2M_⊙) circumstellar material environments prior to core collapse. 

Abstract We present early multiwavelength photometric and spectroscopic observations of the Type IIb supernova SN 2024uwq, capturing its shock-cooling emission phase and double-peaked light-curve evolution. Early spectra reveal broad Hα(v ∼ 15,500 km s⁻¹) and HeIP Cygni profiles of similar strengths. Over time the HeIlines increase in strength while the Hαdecreases, consistent with a hydrogen envelope (M_env = 0.7–1.35M_⊙) overlying helium-rich ejecta. Analytic modeling of early shock cooling emission and bolometric light analysis constrains the progenitor to a partially stripped star with radiusR = 10–60R_⊙, consistent with a blue/yellow supergiant with an initial zero-age main-sequence mass of 12–20M_⊙likely stripped via binary interaction. SN 2024uwq occupies a transitional position between compact and extended Type IIb supernovae, highlighting the role of binary mass transfer efficiency in shaping a continuum of stripped-envelope progenitors. Our results underscore the importance of early UV/optical observations to characterize shock breakout signatures critical to map the diversity in evolutionary pathways of massive stars. Upcoming time-domain surveys, including Rubin Observatory’s LSST and UV missions like ULTRASAT and UVEX, will revolutionize our ability to systematically capture these early signatures, probing the full diversity of stripped progenitors and their explosive endpoints. 

Abstract We present a comprehensive multi-epoch photometric and spectroscopic study of SN 2024bch, a nearby (19.9 Mpc) Type II supernova (SN) with prominent early high-ionization emission lines. Optical spectra from 2.8 days after the estimated explosion reveal narrow lines of H i, He ii, C iv, and N ivthat disappear by day 6. High-cadence photometry from the ground and Transiting Exoplanet Survey Satellite show that the SN brightened quickly and reached a peakM_V ~ −17.8 mag within a week of explosion, and late-time photometry suggests a⁵⁶Ni mass of 0.050M_⊙. High-resolution spectra from days 7.9 and 43 trace the unshocked circumstellar medium (CSM) and indicate a wind velocity of 30–40 km s⁻¹, a value consistent with a red supergiant (RSG) progenitor. Comparisons between models and the early spectra suggest a pre-SN mass-loss rate of $\dot{M}~10^{-3}–10^{-2}{M}_{\odot }{\mathrm{yr}}^{-1}$, which is too high to be explained by quiescent mass loss from RSGs, but is consistent with some recent measurements of similar SNe. Persistent blueshifted H iand [O i] emission lines seen in the optical and near-IR spectra could be produced by asymmetries in the SN ejecta, while the multicomponent Hαmay indicate continued interaction with an asymmetric CSM well into the nebular phase. SN 2024bch provides another clue to the complex environments and mass-loss histories around massive stars. 

Abstract We present multi-epoch optical spectropolarimetric and imaging polarimetric observations of the nearby Type II supernova (SN) 2023ixf discovered in M101 at a distance of 6.85 Mpc. The first imaging polarimetric observations were taken +2.33 days (60085.08 MJD) after the explosion, while the last imaging polarimetric data points (+73.19 and +76.19 days) were acquired after the fall from the light-curve plateau. At +2.33 days there is strong evidence of circumstellar material (CSM) interaction in the spectra and the light curve. A significant level of intrinsic polarizationp_r = 1.02% ± 0.07% is seen during this phase, which indicates that this CSM is aspherical. We find that the polarization evolves with time toward the interstellar polarization level during the photospheric phase, which suggests that the recombination photosphere is spherically symmetric. There is a jump in polarization (p_r = 0.45% ± 0.08% andp_r = 0.62% ± 0.08%) at +73.19 and +76.19 days when the light curve falls from the plateau. This is a phase where polarimetric data are sensitive to nonspherical inner ejecta or a decrease in optical depth into the single-scattering regime. We also present spectropolarimetric data that reveal line (de)polarization during most of the observed epochs. In addition, at +14.50 days we see an “inverse P Cygni” profile in the H and He line polarization, which clearly indicates the presence of asymmetrically distributed material overlying the photosphere. The overall temporal evolution of the polarization is typical for Type II SNe, but the high level of polarization during the rising phase has only been observed in SN 2023ixf. 

Abstract We present supernova (SN) 2023ufx, a unique Type IIP SN with the shortest known plateau duration (t_PT∼ 47 days), a luminousV-band peak (M_V= −​​​​​​18.42 ± 0.08 mag), and a rapid early decline rate (s1 = 3.47 ± 0.09 mag (50 days)⁻¹). By comparing observed photometry to a hydrodynamic MESA+STELLA model grid, we constrain the progenitor to be a massive red supergiant withM_ZAMS∼ 19–25M_⊙. Independent comparisons with nebular spectral models also suggest an initial He-core mass of ∼6M_⊙, and thus a massive progenitor. For a Type IIP, SN 2023ufx produced an unusually high amount of nickel (⁵⁶Ni) ∼0.14 ± 0.02M_⊙, during the explosion. We find that the short plateau duration in SN 2023ufx can be explained with the presence of a small hydrogen envelope ( $M_{{\mathrm{H}}_{\mathrm{env}}}$∼ 1.2M_⊙), suggesting partial stripping of the progenitor. About ∼0.09M_⊙of circumstellar material through mass loss from late-time stellar evolution of the progenitor is needed to fit the early time (≲10 days) pseudo-bolometric light curve. Nebular line diagnostics of broad and multipeak components of [Oi]λλ6300, 6364, Hα, and [Caii]λλ7291, 7323 suggest that the explosion of SN 2023ufx could be inherently asymmetric, preferentially ejecting material along our line of sight. 

ABSTRACT The local distance ladder estimate of the Hubble constant (H0) is important in cosmology, given the recent tension with the early universe inference. We estimate H0 from the Type Ia supernova (SN Ia) distance ladder, inferring SN Ia distances with the hierarchical Bayesian SED model, BayeSN. This method has a notable advantage of being able to continuously model the optical and near-infrared (NIR) SN Ia light curves simultaneously. We use two independent distance indicators, Cepheids or the tip of the red giant branch (TRGB), to calibrate a Hubble-flow sample of 67 SNe Ia with optical and NIR data. We estimate H0 = 74.82 ± 0.97 (stat) $$\pm \, 0.84$$ (sys) km $${\rm s}^{-1}\, {\rm Mpc}^{-1}$$ when using the calibration with Cepheid distances to 37 host galaxies of 41 SNe Ia, and 70.92 ± 1.14 (stat) $$\pm \, 1.49$$ (sys) km $${\rm s}^{-1}\, {\rm Mpc}^{-1}$$ when using the calibration with TRGB distances to 15 host galaxies of 18 SNe Ia. For both methods, we find a low intrinsic scatter σint ≲ 0.1 mag. We test various selection criteria and do not find significant shifts in the estimate of H0. Simultaneous modelling of the optical and NIR yields up to ∼15  per cent reduction in H0 uncertainty compared to the equivalent optical-only cases. With improvements expected in other rungs of the distance ladder, leveraging joint optical-NIR SN Ia data can be critical to reducing the H0 error budget. 

Abstract 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 absoluteB-band peak magnitude of $M_{\max }\left(B\right)\approx -19.16\pm 0.14$mag and a postpeak decline rate of Δm₁₅(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 Siiiand Caiiin 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 Feiiand Niiilines 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. 

Abstract The progenitor system(s) as well as the explosion mechanism(s) of thermonuclear (Type Ia) supernovae are long-standing issues in astrophysics. Here we present ejecta masses and other physical parameters for 28 recent Type Ia supernovae inferred from multiband photometric and optical spectroscopic data. Our results confirm that the majority of SNe Ia showobservableejecta masses below the Chandrasekhar-limit (having a meanM_ej≈ 1.1 ± 0.3M_⊙), consistent with the predictions of recent sub-M_Chexplosion models. They are compatible with models assuming either single- or double-degenerate progenitor configurations. We also recover a sub-sample of supernovae within 1.2M_⊙<M_ej< 1.5M_⊙that are consistent with near-Chandrasekhar explosions. Taking into account the uncertainties of the inferred ejecta masses, about half of our SNe are compatible with both explosion models. We compare our results with those in previous studies, and discuss the caveats and concerns regarding the applied methodology. 

Abstract 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 [Mgii] 4.76μm, [Mgii] 9.71μm, [Neii] 12.81μm, and isolated Oi2.76μm 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. 

Abstract We present high-cadence optical and ultraviolet (UV) observations of the Type II supernova (SN), SN 2022jox which exhibits early spectroscopic high-ionization flash features of Hi, Heii, Civ, and Nivthat disappear within the first few days after explosion. SN 2022jox was discovered by the Distance Less Than 40 Mpc survey ∼0.75 day after explosion with follow-up spectra and UV photometry obtained within minutes of discovery. The SN reached a peak brightness ofM_V∼ −17.3 mag, and has an estimated⁵⁶Ni mass of 0.04M_⊙, typical values for normal Type II SNe. The modeling of the early light curve and the strong flash signatures present in the optical spectra indicate interaction with circumstellar material (CSM) created from a progenitor with a mass-loss rate of $\dot{M}\sim {10}^{-3}\text{–}{10}^{-2}{M}_{\odot }{\mathrm{y}\mathrm{r}}^{-1}$. There may also be some indication of late-time CSM interaction in the form of an emission line blueward of Hαseen in spectra around 200 days. The mass-loss rate of SN 2022jox is much higher than the values typically associated with quiescent mass loss from red supergiants, the known progenitors of Type II SNe, but is comparable to inferred values from similar core-collapse SNe with flash features, suggesting an eruptive event or a superwind in the progenitor in the months or years before explosion.