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Abstract Interacting supernovae probe the twilight years of massive stars, exhibiting signatures of interaction between the supernova ejecta and surrounding material expelled from the progenitor. We present the peculiar interacting supernova, SN 2025ngs in NGC 5961 (37.8 Mpc). This transient toes the line between strongly interacting supernovae (Type IIn) and Type IIP supernovae. SN 2025ngs presents photometrically as a short-plateau supernova, with a plateau durationt ${}_{\mathrm{PT}}^{}\approx 70$ days. Interaction features subside within a week postexplosion, consistent with the growing number of flash supernovae, giving way to a short period where a typical IIP spectrum is exhibited. Towards the drop off the plateau, interaction features re-emerge, exhibiting complex Hαprofiles throughout the rest of the transient evolution. We compare with models of early spectra, finding the abundances generally consistent with a supergiant progenitor with a high mass-loss rate (10⁻³M_⊙yr⁻¹). Early, high-resolution spectra reveal a double-horned Hαprofile, providing strong evidence for shock interaction with a proximate disk-like circumstellar medium. Spectroscopically, SN 2025ngs closely resembles the luminous SN 1998S, despite photometric differences, with SN 2025ngs having a relatively modest peak magnitude ofM_V = −17.9 mag, adding another member to the surprisingly diverse 98S-like group. 

Abstract 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⁻¹and narrow unresolved emission in Civλλ1548.9, 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 byP_shock,abs = 1 × 10⁴¹erg s⁻¹at day 40; SN 2023ixf at day 300 and SN 2024ggi at day 200 are best matched byP_shock,abs = 1 × 10⁴⁰erg s^−1;and SN 2023ixf at day 600 is best matched byP_shock,abs = 5 × 10³⁹erg 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 × 10⁻⁵M_⊙yr⁻¹at 600 yr before explosion to 2 × 10⁻²M_⊙yr⁻¹at 15 yr prior to explosion. For SN 2024ggi, we find a mass-loss rate of 9 × 10⁻⁵M_⊙yr⁻¹at 150 yr before explosion and 1 × 10⁻³M_⊙yr⁻¹at 30 yr before explosion. 

Abstract We present a detailed study of SN 2024ahr, a hydrogen-poor superluminous supernova (SLSN-I), for which we determine a redshift ofz= 0.0861. SN 2024ahr has a peak absolute magnitude ofM_g≈M_r≈ −21 mag, rest-frame rise and decline times (50% of peak) of about 40 and 80 days, respectively, and typical spectroscopic evolution in the optical band. Similarly, modeling of the UV/optical light curves with a magnetar spin-down engine leads to typical parameters: an initial spin period of ≈3.3 ms, a magnetic field strength of ≈6 × 10¹³G, and an ejecta mass of ≈9.5M_⊙. Due to its relatively low redshift, we obtained a high signal-to-noise ratio near-IR (NIR) spectrum about 43 rest-frame days postpeak to search for the presence of helium. We do not detect any significant feature at the location of the Heiλ2.058μm feature and place a conservative upper limit of ∼0.05M_⊙on the mass of helium in the outer ejecta. We detect broad features of Mgiλ1.575μm and Mgiiλ2.136μm, which are typical of Type Ic SNe, but with higher velocities. Examining the sample of SLSNe-I with NIR spectroscopy, we find that, unlike SN 2024ahr, these events are generally peculiar. This highlights the need for a large sample of prototypical SLSNe-I with NIR spectroscopy to constrain the fraction of progenitors with helium (Ib-like) and without helium (Ic-like) at the time of explosion, and hence the evolutionary path(s) leading to the rare outcome of SLSNe-I. 

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 SN 2023ehl, a normal Type Ia supernova with a typical decline rate, was discovered in the galaxy UGC 11555 and offers valuable insights into the explosion mechanisms of white dwarfs. We present a detailed analysis of SN 2023ehl, including spectroscopic and photometric observations. The supernova exhibits high-velocity features in its ejecta, which are crucial for understanding the physical processes during the explosion. We compared the light curves of SN 2023ehl with other well-observed Type Ia supernovae, finding similarities in their evolution. The line strength ratioR(Siii) was calculated to be 0.17 ± 0.04, indicating a higher photospheric temperature compared to other supernovae. The maximum quasi-bolometric luminosity was determined to be 1.52 × 10⁴³erg s⁻¹, and the synthesized⁵⁶Ni mass was estimated at 0.77 ± 0.05M_⊙. The photospheric velocity atB-band maximum light was measured as 10,150 ± 240 km s⁻¹, classifying SN 2023ehl as a normal velocity Type Ia supernova. Our analysis suggests that SN 2023ehl aligns more with both the gravitationally confined detonation, providing a comprehensive view of the diversity and complexity of Type Ia supernovae. 

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 ∼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 ≲ 70 d) spectra indicate interaction between the expanding ejecta and nearby CSM. Att ≲ 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 untilt ≲ 70 d, which suggest continued CSM interaction. We also observe and discuss high-velocity absorption features in Hαand Hβline 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 μm 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 ∼10⁻⁵ M_⊙. 

Abstract We present JWST/Mid-Infrared Instrument (MIRI) and complementary ground-based near-infrared observations of the Type II SN 2017eaw taken 6 yr postexplosion. SN 2017eaw is still detected out to 25μm and there is minimal evolution in the mid-infrared spectral energy distribution (SED) between the newly acquired JWST/MIRI observations and those taken a year earlier. Modeling of the mid-infrared SED reveals a cool ∼160 K dust component of 5.5 × 10⁻⁴M_⊙and a hot ∼1700 K component of 5.4 × 10⁻⁸M_⊙, both composed of silicate dust. Notably, there is no evidence of temperature or mass evolution in the cool dust component in the year between JWST observations. We also present new and archival HST and ground-based ultraviolet (UV) and optical observations which reveal reduced but continued circumstellar medium (CSM)–ejecta interaction at >2000 days postexplosion. The UV and mid-infrared emission show similar decline rates, suggesting both probe the interface between the ejecta and CSM. Given the continued existence of boxy Hαemission in the nebular spectra, the low inferred optical depth of the dust, and the lack of temperature and mass evolution, we suggest that the cool dust component in SN 2017eaw may be primarily due to pre-existing dust rather than newly formed dust in the ejecta or cold dense shell. 

Abstract Supernova (SN) 2025coe at a distance of ∼25 Mpc is the second-closest calcium-strong transient. It was discovered at a large projected offset of ∼34 kpc from its potential host galaxy NGC 3277. Multiband photometry of SN 2025coe indicates the presence of two peaks at day ∼2 and day ∼11 after explosion. Modeling the bolometric light curve, we find that the first peak can be reproduced either by shock cooling of a compact envelope (R_env≈6–40R_⊙;M_env≈0.1–0.2M_⊙) or by interaction with close-in circumstellar material (CSM;R_CSM ≲ 6 × 10¹⁴cm), or a combination of both. The second peak is dominated by radioactive decay of⁵⁶Ni (M_ej ≈ 0.4–0.5M_⊙; $M_{{}^{56}\mathrm{Ni}}\approx 1.4\times 10^{-2}$ M_⊙). SN 2025coe rapidly evolves from the photospheric phase dominated by HeIP Cygni profiles to nebular phase spectra dominated by strong [Caii]λλ7291, 7323 and weak [Oi]λλ6300, 6364 emission lines. Simultaneous line profile modeling of [Caii] and [Oi] at nebular phases shows that an asymmetric core-collapse explosion of a low-mass (≲3.3M_⊙) He-core progenitor can explain the observed line profiles. Alternatively, lack of local star formation at the site of the SN explosion combined with a low ejecta mass is also consistent with a thermonuclear explosion due to a low-mass hybrid He-C/O white dwarf +C/O white dwarf merger. 

Abstract SN 2023ixf was discovered in M101 within a day of the explosion and rapidly classified as a Type II supernova with flash features. Here we present ultraviolet (UV) spectra obtained with the Hubble Space Telescope 14, 19, 24, and 66 days after the explosion. Interaction between the supernova ejecta and circumstellar material (CSM) is seen in the UV throughout our observations in the flux of the first three epochs and asymmetric Mgiiemission on day 66. We compare our observations to CMFGEN supernova models that include CSM interaction ( $\dot{M}<{10}^{-3}$ M_⊙yr⁻¹) and find that the power from CSM interaction is decreasing with time, fromL_sh≈ 5 × 10⁴²erg s⁻¹toL_sh≈ 1 × 10⁴⁰erg s⁻¹between days 14 and 66. We examine the contribution of individual atomic species to the spectra on days 14 and 19, showing that the majority of the features are dominated by iron, nickel, magnesium, and chromium absorption in the ejecta. The UV spectral energy distribution of SN 2023ixf sits between that of supernovae, which show no definitive signs of CSM interaction, and those with persistent signatures assuming the same progenitor radius and metallicity. Finally, we show that the evolution and asymmetric shape of the Mgiiλλ2796, 2802 emission are not unique to SN 2023ixf. These observations add to the early measurements of dense, confined CSM interaction, tracing the mass-loss history of SN 2023ixf to ∼33 yr prior to the explosion and the density profile to a radius of ∼5.7 × 10¹⁵cm. They show the relatively short evolution from a quiescent red supergiant wind to high mass loss. 

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.