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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 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. 

Abstract AT 2019aalc is a peculiar sequence of highly variable emission events observed towards the nucleus of the broad-line active galactic nucleus (AGN) SDSS J152416.66+045119.0. The system exhibited two distinct UV-optical flares (the first detected in 2019, the second one in 2023). Spectra obtained following the detection of the second flare revealed prominent Bowen fluorescence (BF) and high-ionization coronal emission lines, which were much weaker, if at all detectable, in a spectrum taken following the first flare. We present and analyze a large set of multi-wavelength, multi-epoch data for this source, with particular emphasis on optical spectroscopic monitoring conducted with the Las Cumbres Observatory network. During the relatively slow dimming that followed the second optical flare, the UV-optical light curve shows a sequence of minor rebrightening events, while the BF and the coronal lines vary (roughly) in tandem with these “bumps” in the broadband light curve. Most of the observed behavior of AT 2019aalc links it to the growing class of BF flares while setting it apart from canonical tidal disruption events. However, AT 2019aalc has some outstanding peculiarities, including two short flares seen in its soft X-ray light-curve during the dimming phase of the second optical flare, and which do not seem to be linked to the emission line variations. We discuss the optical and X-ray properties of the source and possible scenarios of the origin of the flare, in particular radiation pressure instabilities in the (preexisting) AGN accretion disk. 

A TOM Toolkit plugin module to enable users to send and receive messages via the Hermes astronomical messaging service.  Developed in collaboration with the Scaleable Infrastructure for Multi-Messenger Astrophysics project. 

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. 

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 10⁻⁴yr⁻¹Mpc⁻³h₇₀³), 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 ∼ 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.