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Abstract Episodic mass accretion is the dominant mechanism for mass assembly in the protostellar phase. Although prior optical time-domain searches have allowed detailed studies of individual outbursts, these searches remain insensitive to the earliest stages of star formation. In this paper, we present the characterization of two FU Orionis (FUor) outbursts identified using the combination of the ground-based, near-infrared Wide-field Infrared Transient Explorer (WINTER) and the space-based, mid-infrared NEOWISE survey. Supplemented with near-infrared spectroscopic follow-up, we show that both objects are bona fide FUor type outbursts based on (i) their proximity to star-forming regions, (ii) large amplitude (2–4 magnitudes) infrared brightening over the last decade, (iii) progenitor colors consistent with embedded (Class I) protostars, and (iv) “mixed-temperature” infrared spectra exhibiting characteristic signatures of cool outer envelopes and a hot inner disk with a wind. While one source, WNTR24-cua, is a known FUor that we independently recover; the second source, WNTR24-egv, is a newly confirmed object. Neither source is detected in contemporaneous ground-based optical imaging, despite flux limits ≳100× fainter than their infrared brightness, demonstrating the capabilities of WINTER to identify heavily obscured young stellar object outbursts. We highlight the capabilities of the Galactic Plane Survey of the recently commissioned WINTER observatory in addressing the poorly understood FUor population with its unique combination of real-time detection capabilities, multicolor sensitivity, weekly cadence, and wide area coverage. 

Abstract Electron-capture supernovae (ECSNe) may arise from ONeMg-core collapse in super-asymptotic giant branch (sAGB) stars near the low-mass core-collapse limit (≈8–10M_⊙). At early times, models predict that ECSNe resemble low-mass red supergiant iron-core-collapse SNe, making the two channels difficult to distinguish. Nebular spectroscopy, however, can reveal differences in ejecta composition. We present a systematic sample of 19 nebular spectra of low-luminosity Type IIP (LLIIP) SNe from the Zwicky Transient Facility Census of the Local Universe survey, obtained 115−450 days after explosion. Their low velocities expose narrow lines blended in brighter SNe, which we identify and model to constrain progenitor properties. We find a strong correlation between the FWHM of Hiλ6563 and peak luminosity, showing that LLIIP SNe occupy the low-energy end of the core-collapse population, but no correlation with plateau duration, suggesting that envelope and core properties are not tightly linked. Only one SN reaches the extremely low Hiλ6563 widths predicted for the weakest ∼9M_⊙explosion models, implying that such low-energy events are intrinsically rare. Combining our sample with 118 literature nebular spectra of Type II SNe, we infer an IMF slope of 2.1 ± 1.2. We also introduce an “ECSN score” based on the absence of He- and O-shell emission lines, and identify two plausible ECSN candidates, SN 2023bvj and SN 2024btj. However, neither shows the extremely narrow nebular lines predicted by current ECSN models. If ECSNe arise predominantly through the LLIIP channel, we infer an upper limit on the ECSN rate of ≲(5–8) × 10²Gpc⁻³yr⁻¹, corresponding to a narrow sAGB progenitor mass window of ΔM_sAGB ≲ 0.02–0.06M_⊙. 

Abstract We present WNTR23bzdiq/WTP19aalzlk, a slow eruption of an early-asymptotic giant branch (AGB) star in M31 identified by the Wide-field Infrared Transient Explorer near-infrared (NIR) and the NEOWISE mid-infrared (MIR) surveyors. This source brightened gradually over 7 yr: a 0.5 mag optical rise (2018–2021), a 1 mag optical outburst lasting ∼1000 days (2021–2023), and another 1 mag optical rebrightening in 2024. This was accompanied by a steady MIR brightening of 1 mag over 10 yr in NEOWISE data. Archival optical data show only erratic, small-amplitude (<0.3 mag) brightness variations from 2003 to 2015, revealing a progenitor star withT_eff ≈ 3500 K andL≈ 1.6 × 10⁴L_⊙—consistent with a 7 ± 2M_⊙star in its early-AGB phase. During the eruption, the luminosity rose to ≈5 × 10⁴L_⊙with slow photospheric expansion (≈5 km s⁻¹) and constant temperatures (≈3600 K) inferred from the spectral energy distribution. Optical and NIR spectra of the eruption resemble late M-type stars, with a mixed-temperature behavior—transitioning from M1 in the optical to M7/M8 in the NIR. These properties of WNTR23bzdiq resemble those of stellar merger transients, particularly the giant star merger OGLE-2002-BLG-360, but on longer timescales. As such, WNTR23bzdiq potentially marks the onset of common envelope evolution (CEE) in a binary with an AGB primary, and is possibly a member of the emerging population of infrared transients from CEE in giant stars. Continued multiwavelength monitoring, particularly MIR observations with JWST to quantify dust production, will shed further light on WNTR23bzdiq. 

Abstract With the arrival of ever higher throughput wide-field surveys and a multitude of multi-messenger and multi-wavelength instruments to complement them, software capable of harnessing these associated data streams is urgently required. To meet these needs, a number of community supportedalert brokershave been built, currently focused on processing of Zwicky Transient Facility (ZTF; ∼10⁵–10⁶alerts per night) with an eye toward Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST; ∼2 × 10⁷alerts per night). Building upon the system that successfully ran in production for ZTF’s first seven years of operation, we introduce Burst & Outburst Observations Monitor (BOOM), an analysis framework focused on real-time, joint brokering of these alert streams.BOOMharnesses the performance of aRust-based software stack relying on a non-relationalMongoDBdatabase combined with aValkeyin-memory processing queue and aKafkacluster for message sharing. With this system, we demonstrate feature parity with the existing ZTF system with a throughput ∼7×  higher. We describe the workflow that enables the real-time processing as well as the results with custom filters we have built to demonstrate the system’s capabilities. In conclusion, we present the development roadmap for bothBOOMandBabamul—the public-facing LSST alert broker built atopBOOM—as we begin the Rubin era. 

Abstract Comets and Centaurs trace the evolution of trans-Neptunian objects (TNOs) into the inner solar system. Their activity reflects the interplay between volatile sublimation, dust dynamics, and, in some cases, ring scattering. Yet the long-term behavior of individual objects remains less constrained. To probe this evolutionary transition, we use wide-field survey photometry from the Asteroid Terrestrial-impact Last Alert System (ATLAS), Zwicky Transient Facility, and targeted Las Cumbres Observatory observations of the Jupiter-family comet (JFC) 103P/Hartley 2 during its 2023/24 apparition, and the Centaur (2060) Chiron across 2020–2025, including its 2021 outburst. For 103P, heliocentric activity slopes are asymmetric about perihelion, with a steep inbound index ( $n_{r,\mathrm{pre}}=-3.48\pm 0.08$ ) and flatter outbound value (n_r,post = −1.16 ± 0.04), consistent with enhanced relative dust contribution postperihelion. With reduced brightness versus prior apparitions, this behavior matches reported secular fading trends. Dust mass-loss rates are ∼4–16 kg s⁻¹for assumed grain properties. Colors exhibit a blueward trend near perihelion, consistent with enhanced gas contamination of thegband, with possible phase-dependent scattering. Periodogram analysis recovers a ∼18.7 hr activity-linked period near perihelion. For Chiron, subtracting a quiescent baseline reveals exponential decay from the 2021 outburst on a ∼1.4 yr timescale. Seasonal phase curves flatten fromβ_o = 0.150 ± 0.034 mag deg⁻¹in 2021 to ≲0.09 mag deg⁻¹by 2023–2025, converging with quiescent behavior. Broadband colors remain unchanged at ATLAS (c − o) = 0.22 ± 0.09 mag. The extended duration of this activity suggests a new epoch of persistent, low-level activity and/or evolving ring scattering. These two objects bracket the TNO-to-JFC evolutionary sequence, with 103P near the volatile-depleted end, and Chiron still volatile-rich and capable of episodic activity. 

Abstract 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. 

Abstract 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,AppleCiDErachieves 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. 

Abstract Modern wide-field time-domain surveys facilitate the study of transient, variable and moving phenomena by conducting image differencing and relaying alerts to their communities. Machine learning tools have been used on data from these surveys and their precursors for more than a decade, and convolutional neural networks (CNNs), which make predictions directly from input images, saw particularly broad adoption through the 2010s. Since then, continually rapid advances in computer vision have transformed the standard practices around using such models. It is now commonplace to use standardized architectures pre-trained on large corpora of everyday images (e.g., ImageNet). In contrast, time-domain astronomy studies still typically design custom CNN architectures and train them from scratch. Here, we explore the effects of adopting various pre-training regimens and standardized model architectures on the performance of alert classification. We find that the resulting models match or outperform a custom, specialized CNN like what is typically used for filtering alerts. Moreover, our results show that pre-training on galaxy images from Galaxy Zoo tends to yield better performance than pre-training on ImageNet or training from scratch. We observe that the design of standardized architectures are much better optimized than the custom CNN baseline, requiring significantly less time and memory for inference despite having more trainable parameters. On the eve of the Legacy Survey of Space and Time and other image-differencing surveys, these findings advocate for a paradigm shift in the creation of vision models for alerts, demonstrating that greater performance and efficiency, in time and in data, can be achieved by adopting the latest practices from the computer vision field. 

Abstract Tidal disruption events (TDEs) have traditionally been discovered in optical sky surveys through targeted searches of nuclear transients. However, it is expected that some TDEs will occur outside the galaxy nucleus, arising from wandering black holes (BHs) originating in galaxy mergers. Here, we present observations of TDE 2025abcr, the first optical TDE discovered in the outskirts of a host galaxy. The TDE was identified by a custom “off-nuclear” implementation of the machine learning classifiertdescore, which classifies new ZTF transients based on their lightcurves. Follow-up observations confirm that TDE 2025abcr is a TDE-H+He, occurring 9 $\stackrel{\text{″}}{.}$ 5 (9.3 kpc projected distance) from the nucleus of a massive galaxy (M_⋆= 10^11.18±0.03M_⊙) with a central BH mass of 10^8.82±0.65M_⊙. TDE 2025abcr itself was likely disrupted by a much lighter BH (10^6.09±0.53M_⊙, as estimated with peak luminosity scaling relations). The BH was either dynamically ejected from the nucleus or lies at the center of a very faint tidally stripped dwarf galaxy undergoing a minor merger. Late-time observations of TDE 2025abcr could confirm the origin of this apparent “wandering” BH. The rate of highly offset (≳3 kpc) TDEs can be constrained to <10% of the nuclear TDE rate, but our discovery implies that many dozens of similar sources will be detected by the Vera C. Rubin Observatory each year with resolvable offsets. 

Abstract The Zwicky Transient Facility Census of the Local Universe survey yielded a sample of 330 Type IIP supernovae (SNe) with well-constrained peak luminosities. In paper I, we measured their luminosity function and volumetric rate. Here (paper II), we present the largest systematic study of lightcurve properties for Type IIP SNe from a volume-limited survey, analyzing a selected subset of 129 events, including 16 low-luminosity Type IIP (LLIIP) SNe withM_r,peak≥ −16 mag. We find that plateau slope correlates with peak brightness, with many LLIIP SNe showing positive slopes—suggesting smaller progenitor radii and distinct density profiles compared to brighter Type IIP SNe. The plateau duration shows only a weak dependence on peak brightness, likely suggesting binary interaction. One SN exhibits a plateau-to-tail drop of >3.5 mag, consistent with an electron-capture or failed SN with very low or zero nickel mass. We derive explosion and progenitor parameters of the entire Type IIP SN sample using semi-analytical and radiation-hydrodynamical models. Based on radiation-hydrodynamical model fitting, LLIIP SNe are characterized by low nickel masses (0.001–0.025 M_⊙), low explosion energies (0.1–0.28 × 10⁵¹ erg), low ejecta masses ( $8.1_{-1.7}^{+0.8}$  M_⊙), and ZAMS masses below 11 M_⊙. In comparison, the full Type IIP SN sample spans a wider range with nickel masses (0.001–0.222M_⊙), explosion energies (0.10-4.43 × 10⁵¹erg), ejecta masses (5.4–24.8 M_⊙), and ZAMS masses (9.3-16.7 M_⊙). We find strong correlations between peak brightness, explosion energy, and nickel mass that extend to the low-luminosity end. We conclude that LLIIP SNe represent the faint, low-energy end of the Type IIP population and originate from the lowest-mass core-collapse progenitors.