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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 We present a detailed radio study of the tidal disruption events (TDEs) AT 2020zso and AT 2021sdu. Both exhibit transient radio emission beginning shortly after optical discovery and persisting for several years. For AT 2020zso, we identify two distinct radio flares. The first is detected in the radio ∼22 days after the optical peak, reaching a maximum of ∼1 yr post-discovery before fading. The second flare appears ∼800 days after discovery and results in the brief presence of two distinct components in the radio spectra, providing strong evidence for physically separate outflows. Both flares are consistent with nonrelativistic outflows, with velocities ofv ≈ 0.1–0.2cand energies ofE ∼ 10⁴⁹erg, propagating through a Bondi-like circumnuclear medium. Our analysis supports a scenario in which the first outflow is accretion driven, launched while the TDE disk is accreting at a relatively high Eddington fraction, whereas the second outflow is associated with a transition to an advection-dominated accretion flow. In contrast, the radio emission from AT 2021sdu is best explained by a slower (v ≈ 0.03c), less energetic outflow (E ∼ 10⁴⁸erg), combined with diffuse, nonvariable host emission that becomes dominant ∼500 days after discovery. Assuming free expansion, we infer an outflow launch date preceding the optical discovery date. This suggests that the outflow may originate from either the unbound stellar debris ejected during disruption or, alternatively, from a decelerating outflow. Our findings demonstrate the diversity of outflow properties in TDEs and highlight the observational challenges of interpreting late-time radio variability in the presence of host galaxy contamination. 

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 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 photometric and spectroscopic observations of SN 2024abfl, a low-luminosity Type IIP supernova (LLSN) discovered shortly after explosion. The transient reached a peak absolute magnitude ofM_V = −14.9 and exhibited an extended, flat plateau lasting ∼125 days. From the late-time bolometric light curve, we estimate a⁵⁶Ni mass of ∼0.01M_⊙, consistent with other LLSNe. Analytical shock-cooling models fail to reproduce the rapid early rise, indicating that circumstellar matter (CSM) interaction contributed to the initial emission. The spectroscopic evolution is typical of LLSNe, with relatively narrow metal lines and low expansion velocities (≲3000 km s⁻¹) that decline slowly over time. We detect a broad “ledge” feature around 4600 Å within 3 days of explosion, which we interpret as a blend of high-ionization, shock-accelerated CSM lines. Multipeaked Hαprofiles develop during the plateau phase, consistent with complex ejecta–CSM interaction. As one of the best-observed examples of LLSNe, SN 2024abfl exhibits a weak explosion and signatures of nearby CSM, offering new insights into progenitor properties, pre-explosion mass loss, and the diversity of LLSNe. 

Abstract We present near-infrared (NIR) spectroscopy of the hydrogen- and helium-poor (Type Ic supernovae (SNe Ic)) SN 2024aecx, which displays a strong NIR excess emerging 32 days postpeak. SN 2024aecx is a peculiar SN Ic that exhibited luminous shock-cooling emission at early times, suggestive of close-in circumstellar medium (CSM), unexpected for this class of supernovae (SNe). Its early NIR spectra are typical for a SNe Ic but with strong Ciabsorption features. By ∼32 days postpeak, the spectra show a strong NIR excess, while maintaining normal optical colors, unprecedented for SNe Ic. We find that the NIR excess is well fit with a single-temperature, optically thin dust model with declining temperature, increasing mass, and roughly constant luminosity over time. The NIR excess appears too promptly for dust to have formed in the supernova (SN) ejecta, indicating an IR echo from preexisting dust in the CSM. The IR echo is likely powered by the relatively slowly evolving SN peak light, and not the brief shock cooling emission, as the latter requires unrealistically high CSM densities to explain the observed dust mass. We consider different potential CSM geometries and find that a thick face-on disk with an inner edge of around 5 × 10¹⁶cm can best explain the dust mass and temperature evolution. In this scenario, the SN shock should start interacting with this CSM 440 ± 200 days postexplosion. CSM around SNe Ic is rare, and follow-up observations of SN 2024aecx will probe the mass-loss process responsible for removing hydrogen and helium from its progenitor star. 

Abstract The recent candidate gravitational-wave (GW) alert from a compact object merger involving at least one subsolar mass (SSM) object has prompted questions about their origins. S251112cm is reported by LIGO/Virgo with a false-alarm rate of 1 per 6.2 yr, nearby luminosity distance of 93 ± 27 Mpc, and probability of containing an SSM object of 100%. Such a system, if astrophysical, likely did not involve the supersolar neutron stars or black holes invoked to explain kilonovae. One must then also invoke hitherto unobserved and speculative models to produce SSM mergers that may have electromagnetic (EM) counterparts. We introduce a framework that vets and scores candidate counterparts to SSM GW events to inform follow-up in search of any among the zoo of potential EM transients: kilonovae, kilonovae-within-supernovae, superkilonovae, or active galactic nucleus (AGN) flares from binary black hole mergers. We use a suite of telescopes to perform tiling, galaxy-targeted observations, and photometric/spectroscopic follow-up of promising candidates. In near-real time, we ingest candidates reported by the community, including some of the first observations reported by the Vera C. Rubin Observatory. We vet and score a total of 456 candidates, including 67 from Rubin, but find no likely counterpart. We nonetheless highlight candidates that demonstrate the ability of our framework to distinguish between different transient types and describe strategies to maximize the chances of detecting a counterpart to the next SSM event. Our framework will be implemented in the forthcoming Multimessenger Tool for Rapid Object Vetting and Examination. 

Abstract We present a series of high-resolution echelle spectra of SN 2023ixf in M101, obtained nightly during the first week or so after discovery using PEPSI on the Large Binocular Telescope. NaiD absorption in these spectra indicates a host reddening ofE(B−V) = 0.031 mag and a systemic velocity of +7 km s⁻¹relative to the average redshift of M101. Dramatic changes are seen in the strength and shape of strong emission lines emitted by circumstellar material (CSM), including Heiiλ4686, Civλλ5801,5811, Hα, and Nivλλ7109,7123. In general, these narrow lines broaden to become intermediate-width lines before disappearing from the spectrum within a few days, indicating a limited extent to the dense CSM of around 20–30 au (or ≲10^14.7cm). Hαpersists in the spectrum for about a week as an intermediate-width emission line with P Cyg absorption at 700–1300 km s⁻¹arising in the post-shock shell of swept-up CSM. Early narrow emission lines are blueshifted and indicate an expansion speed in the pre-shock CSM of about 115 km s⁻¹, but with even broader emission in higher-ionization lines. This is faster than the normal winds of red supergiants, suggesting some mode of eruptive mass loss from the progenitor or radiative acceleration of the CSM. A lack of narrow blueshifted absorption suggests that most of the CSM is not along our line of sight. This and several other clues indicate that the CSM of SN 2023ixf is significantly aspherical. We find that CSM lines disappear after a few days because the asymmetric CSM is engulfed by the supernova photosphere. 

Aims.We present optical, ultraviolet, and X-ray observations of supernova (SN) 2024iss, a Type IIb SN that shows a prominent double-peaked light curve. Methods.We modeled the first peak with a semianalytical shock-cooling model and the X-ray emission with a free-free model. We also compared the envelope radius and mass-loss rate with those of other Type IIb SNe to explore the relationships between the progenitor envelope and the circumstellar material. Results.The shock-cooling peak in theV-band light curve reachedM_V = −17.33 ± 0.26 mag, while the⁵⁶Ni-powered second peak attainedM_V = −17.43 ± 0.26 mag. Early spectra show a photospheric velocity of approximately 19 400 km s⁻¹at 3.82 days from the HαP Cygni profile. The Balmer lines persist for at least more than 87 days after the explosion, which is characteristic of hydrogen-rich ejecta. Modeling the first light-curve peak with the shock-cooling model suggests an extended hydrogen envelope with a mass of 0.11 ± 0.04 M_⊙and a radius of 244 ± 43 R_⊙. Fitting the second light-curve peak with an Arnett-like model indicates a typical⁵⁶Ni mass of 0.117 ± 0.013 M_⊙and a relatively low ejecta mass of 1.27 ± 0.34 M_⊙. X-ray observations revealed bright thermal bremsstrahlung emission and indicate a mass-loss rate of 1.6 × 10⁻⁵M_⊙yr⁻¹, which is similar to that of SN 1993J. Conclusions.Supernova 2024iss occupies a transitional position between the two subclasses of extended and compact Type IIb SNe. Its envelope radius and preexplosion mass-loss rate appear to be consistent with the correlation observed in the broader sample. The observational properties of SN 2024iss are compatible with a binary-interaction scenario being the dominant mechanism for envelope stripping.