We present the discovery of SN 2025mkn, a gravitationally lensed Type II supernova. First detected as a blue transient in Zwicky Transient Facility (ZTF), 0."83 from a z = 0.42 elliptical galaxy, the follow-up SNIFS/UH2.2 m and LRIS/Keck spectra revealed absorption lines at z = 1.371. Later JWST NIRCam imaging shows that the bright transient is a close pair of point sources separated by ~ 0."07, and a 30 times fainter counterimage opposite the lens, for which NIRSpec reveals strong Hα emission also at z = 1.371. The lightcurves and spectra are consistent with the Type II supernova source being magnified ≳100 times, with ∼250 required to reconcile its luminosity with that of nearby events such as SN 2023ixf. Lens models are consistent with such high magnifications, and always show that the faint image arrived first (undetected in earlier ZTF imaging), consistent with the later spectral phase of this fainter image. A fourth image is also predicted and possibly detected in the NIRSpec data. Lightcurve-based time-delay measurements are not possible due to the first image being the faintest; however, the resolved NIRSpec spectra offer a future opportunity for time-delay cosmography through supernova phase measurements.

The observational link between long gamma-ray bursts (GRBs) and broad-lined stripped-envelope core-collapse supernovae (SNe Ic-BL) is well established. Significant progress has been made in constraining what fraction of SNe Ic-BL may power high- or low-luminosity GRBs when viewed at small off-axis angles. However, the GRB–SN connection still lacks a complete understanding in the broader context of massive-star evolution and explosion physics. Models predict a continuum of outcomes for the fastest ejecta, from choked to ultrarelativistic jets, and observations from radio to X-rays are key to probing these scenarios across a range of viewing angles and velocities. Here, we present results from a coordinated radio-to-X-ray campaign targeting nearby (z ≲ 0.1) SNe Ic-BL designed to explore this diversity. With eight new radio-monitored events and updated data for one previously observed SN, we further tighten constraints on the fraction of SNe Ic-BL as relativistic as SN 1998bw (GRB 980425). We identify SN 2024rjw as a new radio-loud event likely powered by strong interaction with circumstellar material, and add evidence supporting a similar interpretation for SN 2020jqm. We also establish new limits on the properties of radio-emitting ejecta with velocities consistent with cocoons from choked jets, highlighting SN 2022xxf as a promising cocoon-dominated candidate. These results refine our understanding of the continuum linking ordinary SNe Ic-BL, engine-driven explosions, and GRBs, and contribute to building a sample that will inform future multimessenger searches for electromagnetic counterparts to high-energy neutrinos.

Modern time-domain surveys like the Zwicky Transient Facility (ZTF) and the Legacy Survey of Space and Time (LSST) generate hundreds of thousands to millions of alerts, demanding automatic, unified classification of transients and variable stars for efficient follow-up. We present Applying multimodal learning to Classify transient Detections Early (AppleCiDEr), a novel framework that integrates four key data modalities (photometry, image cutouts, metadata, and spectra) to overcome limitations of single-modality classification approaches. Our architecture introduces (i) two transformer encoders for photometry, (ii) a multimodal convolutional neural network (CNN) with domain-specialized metadata towers and Mixture-of-Experts fusion for combining metadata and images, and (iii) a CNN for spectra classification. Training on ∼30,000 real ZTF alerts, AppleCiDEr achieves high accuracy, allowing early identification and suggesting follow-up for rare transient spectra. The system provides the first unified framework for transients classification using real observational data, with seamless integration into brokering pipelines, demonstrating readiness for the LSST era.

We present the discovery of AT 2024wpp (‘Whippet’), a fast and luminous 18cow-like transient. At a redshift of (Formula presented), revealed by Keck Cosmic Web Imager spectroscopy of its faint star-forming host, it is the fourth-nearest example of its class to date. Rapid identification of the source in the Zwicky Transient Facility data stream permitted ultraviolet-through-optical observations to be obtained prior to peak, allowing the first determination of the peak bolometric luminosity ((Formula presented) erg s(Formula presented) ), maximum photospheric radius ((Formula presented) cm), and total radiated energy ((Formula presented) erg) of an 18cow-like object. We present results from a comprehensive multiwavelength observing campaign, including a far-ultraviolet spectrum from the Cosmic Origins Spectrograph on the Hubble Space Telescope and deep imaging extending (Formula presented) 100 d post-explosion from the Very Large Telescope, Hubble Space Telescope, Very Large Array, and Atacama Large Millimetre Array. We interpret the observations under a model in which a rapidly accreting central engine blows a fast ((Formula presented) 0.2 c) wind into the surrounding medium and irradiates it with X-rays. The high Doppler velocities and intense ionization within this wind prevent identifiable spectroscopic features from appearing in the ejecta or in the surrounding circumstellar material. Weak H and He signatures do emerge in the spectra after 35 d in the form of double-peaked narrow lines. Each peak is individually narrow (full width (Formula presented) km s(Formula presented) ) but the two components are separated by (Formula presented) km s(Formula presented), indicating stable structures of denser material, possibly representing streams of tidal ejecta or an ablated companion star.

We present optical/UV photometric and spectroscopic observations, as well as X-ray and radio follow-up, of the extraordinary event AT2019cmw. With a peak bolometric luminosity of ⁠~ 10^45.6 erg s^-1, it is one of the most luminous thermal transients ever discovered. Extensive spectroscopic follow-up post-peak showed only a featureless continuum throughout its evolution. This, combined with its nuclear location, blue colour at peak and lack of prior evidence of an AGN in its host lead us to interpret this event as a ‘featureless’ tidal disruption event (TDE). It displays photometric evolution atypical of most TDEs, cooling from ~ 30 to ~ 10kK in the first ~ 300 d post-peak, with potential implications for future photometric selection of candidate TDEs. No X-ray or radio emission is detected, placing constraints on the presence of on-axis jetted emission or a visible inner-accretion disc. Modelling the optical light curve with existing theoretical prescriptions, we find that AT2019cmw may be the result of the disruption of a star in the tens of solar masses by a supermassive black hole (SMBH). Combined with a lack of detectable star formation in its host galaxy, it could imply the existence of a localized region of star formation around the SMBH. This could provide a new window to probe nuclear star formation and the shape of the initial mass function (IMF) in close proximity to SMBHs out to relatively high redshifts.

We study AT2024kmq and AT2024lhc, two tidal disruption events (TDEs) with blue featureless spectra associated with high-mass black holes ((Formula presented)). Both events show optical precursors consistent with shock dissipation from stream self-intersection. Their X-ray emission is luminous ((Formula presented)), highly variable (with minimum observed variability time-scales of 1.3 and 4.8 h for factor of ∼3 flux changes), long-lasting (>1 yr), emerging no later than the optical peak, and well characterized by power laws with (Formula presented) (where (Formula presented)). The X-ray properties and radio non-detections support a compact corona ((Formula presented)) producing Comptonized X-ray emission. Using all published featureless TDEs, we find statistically significant bimodality in the distribution of their peak ultraviolet/optical blackbody luminosities and radii. We assemble a comparison TDE sample with early-time X-ray observations with eROSITA, in which we find different (Formula presented) distributions in TDEs with different X-ray spectral evolution properties: low-mass black holes ((Formula presented)) remain soft ((Formula presented)) within (Formula presented) yr, intermediate masses ((Formula presented)) transition from soft to hard at (Formula presented) 1 yr, while high masses ((Formula presented)) are hard ((Formula presented)) from the outset. We interpret this result as evidence that the soft-to-hard state transition in TDEs occurs at the critical threshold of (Formula presented) (similar to X-ray binaries), using the fact that the transition time-scale predicted by simple disc theory scales with black hole mass as (Formula presented).

We present a photometric and spectroscopic analysis of the fast-declining Type II SN 2020aze, observed in optical bands from 2.2 to 137.4 d post-explosion. The V -band light curve reaches a peak absolute magnitude of −16.97 ±0.20 mag by 15 d, followed by a recombination phase with a decline rate of 2 . 04 ±0 . 13 mag (100 d)⁻¹ , lasting ∼120 d. Early spectra ( < 6.0 d) exhibits a transient weak narrow emission line at 4687Åand a bump or ledge feature spanning 4400–4800Å, attributed to narrow and broad blue-shifted He ii λ4686, indicating interaction between the rapidly expanding ejecta and dense circumstellar material (CSM). Spectral comparison with literature models suggests a red supergiant progenitor with a weak wind and a mass-loss rate of∼10⁻³ Myr⁻¹ . Semi-analytical light curve modelling yields an initial radius of 1100 R, an ejecta mass of 12 M, a total explosion energy of 1.5 ×10⁵¹ erg, and a progenitor mass of approximately 14 M. The combination of a steep luminosity decline, early interaction signatures, and an unusually extended photospheric phase highlights the complex interplay between pre-SN mass-loss, CSM interaction, and progenitor properties, positioning SN 2020aze as an important case for understanding the diversity of Type II SNe.

We present X-shooter spectroscopic and photometric observations of a sample of 21 hydrogen-poor superluminous supernovae (SLSNe-I), spanning a redshift range of z = 0.13 − 0.95, aimed at searching for shells of circumstellar material (CSM). Specifically, we focused on identifying broad Mg II absorption features that are blueshifted by several thousand kilometers per second relative to the narrow absorption lines associated with the host galaxy. These broad features have previously been interpreted to arise from resonance line scattering of the SLSN continuum by rapidly expanding CSM ejected shortly before explosion. Utilizing high-quality near-ultraviolet spectra, we modeled the region around 2800 Å to characterize the Mg II line profiles, enabling us to either confirm their presence or place constraints on undetected CSM shells. We identified five objects in our sample that show broad Mg II absorption features consistent with the presence of CSM. While SN 2018ibb, SN 2020xga, and SN 2022xgc have been previously reported, we identified previously undiscovered CSM shells in DES15S2nr and DES16C3ggu. In the case of DES15S2nr, the CSM shell is located at ∼3.4 × 10¹⁵ cm and is moving with a maximum velocity of ∼4800 km s⁻¹. For DES16C3ggu, the shell lies at ∼4.8 × 10¹⁵ cm and reaches up to ∼4700 km s⁻¹. These shells were likely expelled approximately two and three months before the explosion of their respective associated SNe on timescales consistent with late-stage eruptive mass-loss episodes. We further found evidence that the velocities of the CSM shells in all objects lie within 3000 − 5000 km s⁻¹, which may reflect an intrinsic property and could hint at a similar mass-ejection mechanism. We did not find any correlations between the shell properties and the SN properties, except for a marginal correlation between the light curve decline timescale and the shell velocities. This correlation needs further work; however, if it applies, it is a powerful link between the late-time mass ejection and eventual explosion. We further demonstrate that CSM configurations similar to the majority of the detected shells would have been observable in spectra with a signal-to-noise > 5 per resolution element, and that the lines from a shell are, in general, detectable except in cases where the shell is either very geometrically and/or optically thin. Therefore, we conclude that the non-detections are unlikely to arise from selection effects but they may instead point to the existence of a subclass of SLSN-I progenitors undergoing late-stage shell ejections shortly before explosion.

The young supernova remnant SNR 0540-69.3 in the Large Magellanic Cloud offers a detailed view of an energetic pulsar-wind nebula (PWN) interacting with the surrounding ejecta. We present infrared observations of the central region of SNR 0540-69.3 obtained with the JWST NIRSpec and Medium-Resolution Spectrometer integral field units. From the observations we reconstruct the 3D morphology of the strongest emission lines in the inner ejecta (≲1000 km s⁻¹), which reveal the distributions of H I, He I, [Ne ii], [Ne iii], [S iii], [S iv], [Fe ii], and [Ni II]. The 3D morphology of most lines is dominated by two highly fragmented lobes of approximately similar size. Based on the assumption that the lobes are symmetric around the pulsar, we infer a pulsar kick velocity of ∼300 km s⁻¹ away from the observer. There are differences in the 3D morphologies of individual emission lines due to a combination of varying physical conditions and abundances. The detection of H i 1.8756 μm in the inner ejecta confirms the classification of the supernova as a Type II and shows that hydrogen was mixed down to low velocities of <400 km s⁻¹ in the explosion. We compare the results to the Crab Nebula and conclude that asymmetries originating in the explosion most likely play a major role in shaping these PWNe.

Context. The long gamma-ray burst GRB 180728A at a redshift of z = 0.1171 stands out due to its high isotropic energy of E_γ, iso ≈ 2.5 × 10⁵¹ erg, in contrast with most events at redshift z < 0.2, but it is comparable to the bulk of luminous bursts more common at higher redshift.

Aims. We aim to study the properties of GRB 180728A’s prompt emission, afterglow, and associated supernova (SN 2018fip), comparing them with other GRB-SN events.

Methods. This study employs a dense photometric and spectroscopic follow-up of the afterglow and the SN up to 80 days after the burst. We used image subtraction to remove the presence of a nearby bright star, and modelled both the afterglow and the supernova.

Results. This event lies on the E_p, i–E_γ, iso plane occupied by classical collapsar events, and the prompt emission is one of the most energetic at z < 0.2 after GRB 030329 and GRB 221009A. The afterglow of GRB 180728A is less luminous than that of most long GRBs, showing a shallow early phase that steepens after about 5 hours (0.2 days). The GRB exploded in an irregular low-mass blue star-forming galaxy, which is typical of low-z collapsar events. Because of the relatively faint afterglow, the light curve bump of SN 2018fip dominates the optical emission already after approximately 3 days and is one of the best sampled to date. The strong suppression below ∼4000 Å and a largely featureless continuum in the early 6–9 day spectra favour aspherical two-component ejecta with a high-velocity collimated component (> 20 000 km s⁻¹), that is dominant early on and a more massive low-velocity component that dominates at much later epochs.

Conclusions. Our findings indicate that asymmetries need to be considered in order to better understand GRB-SNe. In any case, SN 2018fip shares many characteristics with typical GRB-SNe. Its kinetic energy is below the common range of 10⁵²–10⁵³ erg and does not correlate with the high energy of the GRB, highlighting the complexity and diversity of the GRB-SN energy budget partition.