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Abstract We present a comprehensive optical and near-infrared (NIR) spectroscopic study of SN 2024afav, a hydrogen-poor superluminous supernova (SLSN-I) that peaks at ≈−20.7 mag and exhibits an unusual multibumped light curve. Our spectroscopic observations, spanning phases of −14 to +160 days, reveal several unusual features: (i) a narrow (1800 km s⁻¹) and blueshifted (11,000 km s⁻¹) absorption from Hαstarting at +20 days; (ii) persistent optical and NIR Heilines at all available phases, showing double absorption structure in NIR spectra at +23 days, with a high-velocity component at a similar velocity to Hα; (iii) early appearance of nebular [Oiii] emission starting at ≈+50 days; and (iv) a strong [Oii] + [Caii] 7300 Å emission complex starting at ≈+110 days. These unusual features, and their onset at the time of the light-curve bumps, provide compelling evidence of circumstellar interaction between the SN ejecta and a nearby hydrogen-rich shell, as well as the presence of helium in both the outer layers of the progenitor star and the circumstellar medium. A comparison of SN 2024afav to other SLSNe-I showing bumpy light curves and similar spectral properties (PTF 10hgi, SN 2017egm, SN 2019hge) points to a rare subgroup of SLSNe-I in which circumstellar medium interaction provides an important modulation to the energy input. 

Abstract Calcium-strong transients (CaSTs) are a subclass of faint and rapidly evolving supernovae (SNe) that exhibit strong calcium features and notably weak oxygen features. The small but growing population of CaSTs exhibits some aspects similar to thermonuclear SNe but others similar to massive star core-collapse events, leading to intriguing questions on their physical origins. SN 2025coe is one of the nearest CaSTs discovered to date, and our coordinated multiwavelength observations obtained days to weeks postexplosion reveal new insights into these enigmatic transients. With the most robust near-IR (NIR) spectroscopic time series of a CaST collected to date, SN 2025coe shows spectral signatures characteristic of Type Ib SNe (SNe Ib; i.e., He-rich stripped-envelope SNe (SESNe)). SN 2025coe is the third X-ray-detected CaST and our analysis of Neil Gehrels Swift Observatory X-ray data suggests interaction with 0.12 ± 0.11M_⊙of circumstellar material (CSM) extending to at least 2 × 10¹⁵cm (∼30,000R_⊙), while our analysis of the 1–240 GHz radio nondetections gives an outer radius of that CSM of at most ∼5 × 10¹⁵cm. This inferred nearby high-density CSM extending out to (3.5 ± 1.5) × 10¹⁵cm is similar to that seen in the other two X-ray-detected CaSTs, and its presence suggests that either intensive mass loss from a massive star or some exotic pre-SN mass ejection may be a common feature of this subclass. Our work also expands upon recent studies of the optical properties of SN 2025coe and explores our current understanding of different progenitor systems that could possibly produce CaSTs. 

Abstract 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 Hαabsorption with HeIcontamination, 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 ∼0.6–0.8M_⊙—significantly larger than canonical IIb values (≲0.1M_⊙) but consistent with the ∼0.9M_⊙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. 

Abstract We present extensive ultraviolet, optical, and near-infrared (NIR) photometric and spectroscopic observations of the nearby hydrogen-poor superluminous supernova (SLSN-I) SN 2024rmj atz= 0.1189. SN 2024rmj reached a peak absolute magnitude ofM_g ≈ −21.9, placing it at the luminous end of the SLSN-I distribution. The light curve exhibits a pronounced prepeak bump (≈60 days before the main peak) and a postpeak bump (≈55 days after the main peak). The bulk of the light curve is otherwise well fit by a magnetar spin-down model, with typical values (spin: ≈2.1 ms; magnetic field: ≈6 × 10¹³G; ejecta mass: ≈12M_⊙). The optical spectra exhibit characteristic SLSN-I features and evolution, but with a relatively high velocity of ≈8000 km s⁻¹postpeak. Most significantly, we find a clear detection of helium in the NIR spectra at Heiλ1.083μm andλ2.058μm, blueshifted by ≈15,000 km s⁻¹(13 days before peak) and ≈13,000 km s⁻¹(40 days after peak), indicating that helium is confined to the outermost ejecta; based on these NIR detections, we also identify likely contribution from Heiλ5876 in the optical spectra on a similar range of timescales. This represents the most definitive detection of helium in a bright SLSN-I to date, and indicates that progenitors with a thin helium layer can still explode as SLSNe. 

ABSTRACT We present high-cadence photometric and low-resolution (R  $$\sim$$ 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 $$-16.42 \pm 0.01$$ mag at 50 d, resembles normal-luminous supernova, and the V-band decline rate of 0.42 $$\pm$$ 0.06 mag 50 d$$^{-1}$$ during the plateau phase. A steeper decline rate of 11.87 $$\pm$$ 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 $$\sim$$11 $${\rm M}_\odot$$ and an initial radius of 424 $${\rm R}_\odot$$. On the contrary, hydrodynamical modelling suggests a higher mass progenitor between 14 and 16 $${\rm M}_\odot$$. 

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 long-term photometric and spectroscopic studies of circumstellar material (CSM)–ejecta interacting supernova (SN) ASASSN-14il in the galaxy PGC 3093694. The SN reaches a peakr-band magnitude of ∼−20.3 ± 0.2 mag, rivaling SN 2006tf and SN 2010jl. The multiband and the pseudo-bolometric lightcurves show a plateau lasting ∼50 days. Semi-analytical CSM interaction models can match the high luminosity and decline rates of the lightcurves but fail to faithfully represent the plateau region and the bumps in the lightcurves. The spectral evolution resembles a typical Type IIn SN dominated by CSM interaction, showing blue continuum and narrow Balmer lines. The lines are dominated by electron scattering at early epochs. The signatures of the underlying ejecta are visible as the broad component in the Hαprofile from as early as day 50, hinting at asymmetry in the CSM. A narrow component is persistent throughout the evolution. The SN shows remarkable photometric and spectroscopic similarity with SN 2015da. However, the different polarization in ASASSN-14il compared to SN 2015da suggests an alternative viewing angle. The late-time blueshift in the Hαprofile supports dust formation in the post-shock CSM or ejecta. The mass-loss rate of 2–7M_⊙yr⁻¹suggests a luminous blue variable progenitor in an eruptive phase for ASASSN-14il. 

We conducted an exhaustive analysis combining optical photometry and spectroscopy of the type Ia supernova designated SN 2023xqm. Our observational period spanned from the two weeks preceding to 88 days after theB-band peak luminosity time. We determined the peak brightness in theB-band to be −18.90 ± 0.50 mag, and it is accompanied by a moderately slow decay rate of 0.90 ± 0.07 mag. The maximum quasi-bolometric luminosity was estimated to be 1.52 × 10⁴³erg s⁻¹and correlated with a calculated⁵⁶Ni mass of 0.74 ± 0.05M_⊙, aligning with the modestly reduced rate of light curve decay. A plateau that can be observed in ther − icolor curve might correlate with the minor elevation noted between the principal and secondary peaks of thei-band light curve. An initial spectral analysis of SN 2023xqm revealed distinct high-velocity features (HVFs) in Ca IIthat contrast with the subdued HVFs observed in Si II. Such attributes may stem from variations in ionization or temperature or from scenarios involving enhanced element abundance, suggesting a naturally lower photospheric temperature for SN 2023xqm, which could be indicative of incomplete burning during the white dwarf’s detonation. The observed traits in the light curve and the spectral features offer significant insights into the variability among type Ia supernovae and their explosion dynamics. 

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 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.