Daniel A. Perley

We present the discovery and characterization of SN 2018erx (ZTF18abkmbpy), a fast-evolving, unusually red, interacting stripped-envelope supernova. Spectroscopically, SN 2018erx exhibits prominent broad C ii emission with characteristic widths of ∼3800 km s ⁻¹ , consistent with interaction with a carbon-rich circumstellar medium (CSM) and a Type Icn core-collapse SN classification. Photometrically, SN 2018erx evolves exceptionally rapidly, rising from half-maximum to peak in 2.1 days and declining back in 3.1 days, placing it among the fastest-evolving core-collapse supernovae observed. Semi-analytical CSM-interaction modeling favors a compact, shell-like CSM with M _CSM ≈ 0.3 M _⊙ , an inner radius of R ₀ ≈ 0.7 au, and a very low ejecta mass of M _ej ≈ 0.11 M _⊙ . The radioactive yield is likewise small, with a ⁵⁶ Ni mass ≲(3–5) × 10 ⁻³ M _⊙ , placing SN 2018erx at the low end of the H-poor stripped-envelope SN distribution. At +29 days after peak, we detect a near-infrared excess consistent with pre-existing local circumstellar dust and infer a hot-dust mass of M _d ∼ 10 ⁻⁶ –10 ⁻⁵ M _⊙ . Taken together, the rapid evolution, strong local reddening, carbon-rich emission, and evidence for pre-existing dust point to a multi-component circumstellar environment consisting of a dense inner interaction region produced by enhanced pre-SN mass loss ( M ̇ ∼ 1 0 − 4 –10 ⁻³ M _⊙ yr ⁻¹ ) and an outer dusty layer at R ≳ 4 × 10 ¹⁶ cm, produced by an earlier mass-loss episode roughly 10–200 yr before core collapse. These properties favor an ultra-stripped core-collapse explosion of a low-mass He star in a binary system that underwent late-time Case BC mass transfer or Si-flash-induced mass loss. Fallback-modified Wolf–Rayet collapse or a merger-driven mass-loss episode remain plausible alternatives. These observations provide rare insight into the mass-loss history of stripped-envelope SNe, indicate that SN 2018erx-like events may be efficient sites of dust formation, and suggest that dust-enshrouded explosions of this kind may be systematically underrepresented in optical surveys.

The luminous fast blue optical transient (LFBOT) AT2022tsd exhibited minutes-timescale optical flares in the tens of days following the initial transient event, likely due to a central engine—either an accreting black hole or a magnetar. In this paper, we use data from the Transiting Exoplanet Survey Satellite (TESS) and the Zwicky Transient Facility (ZTF) to constrain the occurrence of similar flares in the 12 (of 14) known LFBOTs that had observational coverage with TESS from tens to thousands of days after the transient’s initial emission. We find seven flare-like signals at the locations of four unique LFBOTs; all seven can likely be attributed to a solar system object (SSO) moving through the TESS aperture. Assuming all seven flares arise from SSOs, for the LFBOT AT2024qfm we rule out flaring with a similar timescale (40–65 days) and luminosity ( νL _ν ∼ 10 ⁴³ erg s ⁻¹ ) as in AT2022tsd, while for AT2022tsd itself we rule out flares between 380 and 430 days after the initial transient that were as luminous as the earlier flares. This observation suggests that the engine power in AT2022tsd declined or shut off on a timescale of hundreds of days. We also find that there is no late-time activity detectable in TESS thousands of days after the prototype LFBOT, AT2018cow. We discuss our constraints on the duty cycle of such flaring and then present estimates for the number of minutes-duration flares detectable with ongoing and upcoming high-cadence (≪1 day) wide-field surveys.

The Type I super-luminous supernova SN 2024jlc (ZTF24aapadbb) exploded on 25 May 2024 at z = 0.039. This was the closest supernova of this class discovered in recent years and one of the closest ever. It therefore represented a rare opportunity to study this type of object in detail. We performed a multiwavelength analysis that spanned ten orders of magnitude in frequency and included optical and UV photometry and spectroscopy, soft and hard X-rays, and high-energy γ -rays. We characterized the event as a slow-evolving and He-rich supernova, with one of the lowest peak luminosities reported for a super-luminous event M _g ∼ −19.37 mag, and a light-curve evolution compatible with either a circumstellar interaction and a magnetar spin-down model, with noticeable contribution from ⁵⁶ Ni decay. No significant excess was found in the soft and hard X-ray bands, for which we provide upper limits on the flux. Additionally, we analyzed two years of Fermi -LAT data, from which we report an intriguing hint of a γ -ray signal at the ∼3.6 σ level, although no firm detection can be claimed. The ratio of gamma to optical efficiency, η = 0.38, suggests a central-engine scenario, similar to SN 2017egm. Our analysis suggests that SN 2024jlc might bridge the gap between super-luminous supernovae and classical stripped-envelope supernovae. While still poorly populated, this bridge might consist of all super-luminous Ib supernovae, with the key difference residing in the powering mechanism.

In 2026 March, the Einstein Probe (EP) discovered its nearest ( z = 0.0343) Fast X-ray Transient (FXT), EP 260321a, the first EP FXT to provide a strong match to expectations for X-ray “shock breakout” (SBO) emission. Here, we present our multiwavelength follow-up campaign of EP 260321a and its broad-line Type Ic (Ic-BL) supernova (SN) counterpart, SN 2026gzf. We show that our radio follow-up extending over 5.8–54.5 days post-FXT rules out an on-axis jet counterpart of isotropic-equivalent kinetic energy E _K ≳ 10 ⁴⁹ erg for circumburst densities n > 10 ⁻² cm ⁻³ and assuming microphysical parameters ϵ _e = ϵ _B = 0.1. Our radio data also constrain a median mass-loss rate of M ̇ ≲ 1.2 × 1 0 − 5 M ⊙ yr − 1 for a Wolf–Rayet progenitor. In addition, we derive SN 2026gzf’s properties, including ⁵⁶ Ni mass, diffusion timescale, and expansion velocities, from our ∼nightly cadence optical data and compare them with those of optically discovered Type Ic-BL SNe, finding that SN 2026gzf is well within the 90% confidence interval across all properties. We further fit SN 2026gzf’s light curve and determine that combined emission from both interaction with CSM and ⁵⁶ Ni radioactive decay provides the best fit with plausible model parameters. Finally, using the rate of Ic-BL SNe from the Zwicky Transient Facility Bright Transient Survey and assuming all Type Ic-BL SNe produce EP 260321a-like FXTs, we infer an expected rate of EP-detected SBOs of 4.4–16 yr ⁻¹ . This is inconsistent at the 90% confidence level with current EP detection rates, potentially indicating that most Type Ic-BL SNe produce less luminous X-ray SBO signals compared to EP 260321a.

We present early (≲1 yr) multiwavelength observations and analysis of six luminous fast blue optical transients (LFBOTs). We identified these LFBOTs in Zwicky Transient Facility survey data from their fast light-curve evolution ( t _1/2 ≤ 12 days), blue colors at peak brightness ( g − r ≤ −0.2 mag), a visible host galaxy, high optical luminosity ( M _g < −20 mag), and an X-ray and/or radio detection. With the exception of AT2024aehp (ZTF24abygbss), these transients exhibit peaks in their 10 GHz radio light curves at t _rest ≈ 50–100 days, with peak radio luminosities ranging from 10 ³⁸ to 10 ⁴⁰ erg s ⁻¹ . Modeling the radio emission as synchrotron radiation indicates a fast ( v = 0.1–0.3 c ) shock in a dense ( n _e ≈ 10 ³ –10 ⁴ cm ⁻³ ) medium. The X-ray emission varies by ≈2 orders of magnitude in luminosity (10 ⁴² –10 ⁴⁴ erg s ⁻¹ ) at t _rest ∼ 20 days. Analysis of the host-galaxy photometry and spectroscopy for each transient shows that LFBOTs are predominantly nonnuclear (a few kiloparsecs offset) with star-forming host galaxies of stellar masses = 10 ⁹ –10 ¹¹ M _⊙ . Unlike all other LFBOTs to date, AT2024aehp exhibited a luminous ( M < −19 mag) plateau in the optical light curve and its 6–15 GHz radio emission brightened by over an order of magnitude from t _rest ≈ 70 to 130 days. The mostly consistent radio behavior between these LFBOTs implies a similar circumburst medium, leading us to prefer a progenitor scenario in which mass is lost in a consistent way shortly prior to the terminal event.

We present the discovery of EP250827b/SN 2025wkm, an X-ray flash (XRF) discovered by the Einstein Probe (EP), accompanied by a broad-line Type Ic supernova (SN Ic-BL) at z = 0.1194. EP250827b possesses a prompt X-ray luminosity of ∼10 ⁴⁵ erg s ⁻¹ , lasts over 1000 s, and has a peak energy E _p < 1.5 keV at 90% confidence. SN 2025wkm possesses a double-peaked optical light curve (LC), though its bolometric luminosity plateaus after its initial peak for ∼20 days, consistent with a central engine injecting additional energy into the explosion. Its spectrum transitions from a blue to red continuum with clear blueshifted broad absorption features consistent with a SN Ic-BL classification. We do not detect any transient radio emission and rule out the existence of an on-axis, energetic jet ≳10 ⁵⁰ erg assuming a typical LGRB circumburst constant density ( n ≈ 10 ⁻³ –10 ⁻¹ cm ⁻³ ) and microphysical parameters ( ϵ _e = 0.1 and ϵ _B = 0.01). In the model we invoke, the collapse gives rise to a long-lived magnetar, potentially surrounded by an accretion disk. Magnetically driven winds from the magnetar and the disk mix together and break out with a velocity ∼0.35 c and interact with an extended circumstellar medium with radius ∼10 ¹³ cm, generating X-ray breakout emission through nonthermal free–free processes. The disk outflows and magnetar winds power blackbody photospheric emission as they cool adiabatically and thermalize, producing the first SN peak. The spin-down luminosity of the magnetar and radioactive decay of ⁵⁶ Ni power the late-time emission. We end by discussing the landscape of XRF-SNe within the context of EP’s recent discoveries.

Context. Current large-scale, high-cadence surveys, such as the Zwicky Transient Facility (ZTF), provide detections of new and rare types of transients and supernovae (SNe) whose physical origins are not well understood. Aims. We aim to investigate the nature of SN 2021lwz at a redshift z = 0.065, an over-luminous SN with an absolute magnitude of M _g ∼ −20.1 AB that falls in the lower range of superluminous supernovae (SLSNe) luminosities and was discovered in a faint dwarf galaxy with an absolute magnitude of M _g ≃ −14.5 AB. Methods. We studied SN 2021lwz using optical spectroscopy and photometry and by imaging linear polarimetry obtained during several follow-up campaigns. All the data were used to analyse and model the evolution of the explosion. Comparisons with other SNe of well-known or rarer types were investigated. Results. SN 2021lwz belongs to the rare class of rapidly evolving transients. The bolometric light curve rises in about seven days to a peak luminosity of about 5 × 10 ⁴³ erg/s, at a rate of 0.2 mag day ⁻¹ close to the peak. Spectroscopy modelling reveals more similarities with a normal Type Ic-like SN than with an SLSN before peak, showing slightly broadened lines after peak. Light curve modelling shows that the Arnett model of the bolometric light curve using a radioactive source ( ⁵⁶ Ni) is not able to reasonably explain the light curve evolution. A magnetar model seems more appropriate, suggesting that the explosion of low ejecta mass ( M _ej ∼ 0.24 M _⊙ ) took place in a low-mass ( M ∼ 10 ^6.66 M _⊙ ) dwarf galaxy of specific star formation rate about ten times larger than typical star-forming galaxies. Conclusions. SN 2021lwz is an uncommon transient showing many similarities with several classes of transients, including rare transients. It may be an interesting example of how differences in ejecta mass and engine parameters could produce a wide range of engine-driven stripped-envelope SNe.

Luminous fast blue optical transients (LFBOTs) are a growing class of enigmatic energetic transients. They show fast rises and declines, high temperatures throughout their evolution, and non-thermal emission in radio and X-rays. Their power source is currently unknown, but proposed models include engine-driven supernovae, interaction-powered supernovae, shock cooling emission, intermediate mass black hole tidal disruption events (IMBH TDEs), and Wolf-Rayet/black hole mergers, among others. AT2024wpp is the most optically luminous LFBOT to date and has been observed extensively at multiple wavelengths, including radio, optical, UV, and X-rays. We take models from multiple scenarios and fit them to the AT2024wpp optical, radio, and X-ray light curves to determine which of these scenarios can best describe all aspects of the data. We show that none of the multiwavelength light curve models can reasonably explain the data, and that other physical arguments disfavour models with homologously expanding ejecta. We discuss how a stellar mass/IMBH TDE of a low mass star can be tested with late-time observations, and what other scenarios could possibly explain the broadband data.

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 H α 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.