Steven Schulze

Direct observational constraints on the earliest phases of galactic outflows remain scarce. We present Very Large Telescope/X-shooter spectroscopy of seven Type I superluminous supernova (SLSN-I) host galaxies at z = 0.15−0.51, exploiting the bright SLSN continua as down-the-barrel probes of the host interstellar medium. Five of the seven hosts exhibit narrow, blueshifted Mg II λλ 2796, 2803 absorption, indicative of the presence of low-ionized outflows. Voigt modeling of the Mg II absorption yields bulk outflow velocities of 45−99 km s ⁻¹ and terminal velocities of v max ≃ 103 − 164 km s − 1 , the latter being below the ones reported for more evolved galaxies of similarly low mass and star formation rate. Given the expected short lifetimes of massive SLSN progenitors, we argue that these outflows are most naturally explained as originating during the preceding stellar-wind-dominated phase. We derive wind masses of M _wind ≃ 10 ⁴ −10 ⁵ M _⊙ , mass outflow rates comparable to or lower than the star formation rates, and kinetic energies of 10 ⁵¹ −10 ⁵² erg. These energies represent only a modest fraction (≃10%) of the mechanical energy expected from stellar winds during the first few Myr, demonstrating that the observed outflows can be powered entirely by presupernova feedback. Together with their low terminal velocities, these results support a scenario in which stellar winds and radiation pressure dominate the early acceleration of cold outflows, before core-collapse supernovae become dynamically important. Our work provides one of the first empirical constraints on early feedback phases relevant for high-redshift galaxies and for time-dependent implementations of stellar feedback in galaxy formation simulations.

The candidate gravitational wave (GW) event S250818k was one of only three non-retracted LIGO-Virgo-KAGRA public alerts issued during the fourth observing run of the network (O4) with a binary neutron star (BNS) merger classification probability exceeding one percent. This triggered a prompt search for a potential electromagnetic (EM) counterpart in the large localization error region (949 deg ² projected in the sky at the 90% credible level). The transient supernova (SN) 2025ulz discovered by the Zwicky Transient Facility (ZTF) during the search, attracted a great deal of attention due to a potential spatial and temporal coincidence, and due to its initial fast decay and featureless spectrum. Here, we report on the follow-up of this transient by the Electromagnetic counterparts of gravitational wave sources at the Very Large Telescope (ENGRAVE) Collaboration. We conducted an extensive multi-wavelength observational campaign, which led to the spectral classification of the transient as a type IIb SN, indicating that it is unrelated to the candidate GW event. In this article, we describe our observing strategies, data reduction, and interpretation. All of our results confirm and strengthen our classification of the source, and also show that shock-cooling tails associated with type IIb SNe are one of the most prominent contaminants in kilonova searches.

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.

We investigate the thermal emission and the extinction from dust associated with the nearby ( z = 0.0267) superluminous supernova (SLSN) 2018bsz. Our dataset combines daily cadence, simultaneous optical and near-infrared (NIR) coverage up to ∼100 days with late-time (+ 1.7 yr) mid-infrared (MIR) observations. At 230 days after the light-curve peak, the supernova (SN) is not detected in the optical, but shows a surprisingly strong NIR excess, with r − J > 3 mag and r − K _s > 5 mag. The temporal evolution of the infrared (IR) light curve allows us to assess whether the MIR emission originates from newly formed dust, either in the SN ejecta or in a postshock circumstellar shell, or instead from an IR echo produced by preexisting circumstellar or interstellar dust heated by the SN radiation. Our radiative-transfer modeling shows that the circumstellar and interstellar echo scenarios cannot simultaneously reproduce the observed IR luminosity and its temporal evolution, and we therefore disfavor these interpretations. In contrast, a scenario in which new dust forms in the SN ejecta at epochs ≳200 days provides a self-consistent explanation for the evolution of the SN flux. We can fit the spectral energy distribution well at +230 days with 5 × 10 ⁻⁴ M _⊙ of carbon dust, increasing over the following several hundred days to 10 ⁻² M _⊙ by +535 days. SN 2018bsz is the first SLSN showing evidence for dust formation within the SN ejecta, and appears to form 10 times more dust than normal core-collapse supernovae (SNe) at similar epochs. Together with their preference for low-mass, low-metallicity host galaxies, we suggest that superluminous SNe may be a significant contributor to dust formation in the early Universe.

We present multiwavelength observations and analysis of SN 2024iss, a Type IIb supernova (SN IIb) located at ∼14 Mpc. The first Zwicky Transient Facility detection of SN 2024iss is ∼40 minutes after first light (one of the earliest detections of a SN IIb to date) and a Hubble Space Telescope (HST) UV spectrum was obtained at 7 days (the earliest HST UV SN IIb spectrum to date). We estimate an ejecta mass range of 1.1–3.3 M _⊙ and a ⁵⁶ Ni mass of 0.11 ± 0.01 M _⊙ from bolometric light-curve modeling and He-star model comparisons. We fit shock-cooling emission models to estimate a progenitor radius of 100–320 R _⊙ and an envelope mass of 0.07–0.46 M _⊙ . We compare optical/UV spectra to binary progenitor models, which indicate a stripped H-rich envelope mass of 0.19–0.28 M _⊙ . We use early-time X-ray detections to calculate circumstellar material (CSM) densities that are consistent with a progenitor mass-loss rate of 5 × 10 ⁻⁴ M _⊙ yr ⁻¹ ( v _w = 100 km s ⁻¹ ), corresponding to 2–5 yr preexplosion. In the UV, we observe strong Mg ii emission extending to 15,000 km s ⁻¹ as well as weak P Cygni profiles of iron-group elements (e.g., Fe, Ti, Al, Ni) present in outer SN ejecta. The overall spectroscopic evolution of SN 2024iss is comparable to that of SNe IIb, but its increased brightness at peak is influenced by SN ejecta–CSM interaction. Nebular spectroscopy of SN 2024iss at ∼260–412 days reveals multipeaked forbidden-line profiles of O i and Mg i ] indicative of inner ejecta asymmetry and/or clumping. We demonstrate the utility of a rich, multiwavelength data set for constraining the progenitor systems and explosion dynamics of SNe IIb.

We present optical and near-infrared (NIR) observations of the Type Ib supernova (SN) 2024rbc. Emission from the first CO overtone, resting on a dust continuum at 2.3−2.4 μ m, was observed at 62 days postexplosion. The CO band heads are not resolved, and the emission appears broad, lacking sharp spectral features. This is the first observation of CO in the ejecta of a Type Ib SN reported in literature. The spectra of SN 2024rbc exhibit strong He I lines and numerous neutral and ionized metal lines. Comparing the spectral evolution of SN 2024rbc to other Type Ib, Ic, and IIb SNe indicates it is a Type Ib SN. We compare the velocities of key optical lines to examine the evolution of the ejecta. Additionally, fitting SN light-curve models of helium star progenitors computed with the STELLA code to photometric observations indicates a ⁵⁶ Ni mass of 0.07 M _⊙ and an ejecta mass of 1.7 M _⊙ . Fitting an LTE model to the CO overtone implies a CO mass of 5.2 × 10 ⁻⁴ M _⊙ , a CO temperature of 4040 K, and a CO velocity width of 5905 km s ⁻¹ . We also fitted a modified blackbody model to the dust continuum, deriving a dust temperature of 910 K and a dust mass of 1.3 × 10 ⁻³ M _⊙ . The CO provides direct evidence for the onset of dust formation, and the observed dust continuum likely originates from newly formed dust in the ejecta. However, robust dust mass estimates require mid-infrared (MIR) observations.

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.

Superluminous supernovae (SLSNe) are one of the most luminous stellar explosions known, yet they remain poorly understood. Because they are intrinsically rare, efficiently identifying them in the large alert streams produced by modern time-domain surveys is essential for building larger observational samples and enabling spectroscopic follow-up. We present NOMAI, a machine-learning classifier designed to identify SLSN candidates directly from photometric alerts in the ZTF stream, using light curves accumulated over at least 30 days. It does not require any spectroscopic redshift and is running in real time within the Fink broker. ZTF light curves were transformed into a set of physically motivated features derived primarily from model-fitting procedures using SALT2 and Rainbow, a blackbody-based multiband fitting framework. These features were used to train an XGBoost classifier on a curated dataset of labeled ZTF sources constructed using literature samples of SLSNe, along with TNS and internal ZTF labeled sources. The final dataset contains 5280 unique sources, including 225 spectroscopically classified SLSNe. Averaged over 100 bootstrap realizations, the classifier reaches 66% completeness and 58% purity. Deployed within the Fink broker, NOMAI has been running continuously since 18 December 2025 on the ZTF alert stream and publicly reports SLSN candidates every night by automatically posting them to dedicated communication channels. Based on this, we also report the first two-month evaluation period, where the classifier successfully recovered 22 of the 24 active SLSNe reported on the Transient Name Server, providing an upper limit on its real-time completeness. The achieved performances, particularly the high completeness in real-time operations, demonstrate that the classifier provides a valuable tool for experts to efficiently scan the alert stream and identify promising candidates. In the near future, NOMAI is intended to be adapted to operate on the Legacy Survey of Space and Time conducted by the Vera C. Rubin Observatory, which is expected to uncover an unprecedented number of transients, making machine-learning based photometric classification essential.