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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 follow-up of gravitational-wave events by wide-field surveys is a crucial tool for the discovery of electromagnetic counterparts to gravitational wave sources, such as kilonovae. Machine learning tools can play an important role in aiding search efforts. We have developed a public tool to predict kilonova light curves using simulated low-latency alert data from the International Gravitational Wave Network during observing runs 4 (O4) and 5 (O5). It uses a bidirectional long-short-term memory model to forecast kilonova light curves from binary neutron star and neutron star–black hole mergers in the Zwicky Transient Facility (ZTF) and Rubin Observatory’s Legacy Survey of Space and Time filters. The model achieves a test mean squared error (MSE) of 0.12 for ZTF filters and 0.23 for Rubin filters, calculated by averaging the squared error over all time steps, filters, and light curves in the test set. We evaluate the performance of the model against merger events followed-up by the ZTF partnership during O4c. We also analyze the effect of incorporating constraints on physical features such as ejecta mass. Using ejecta mass, the performance of the model improves to an MSE of 0.1 for ZTF filters and 0.15 for Rubin filters. Our model is publicly available and can help to add important information to help plan follow-up of candidate events discovered by current and next-generation public surveys. 

Abstract We report on the prediscovery observations and constraints of the new interstellar comet 3I/2025 N1 (ATLAS), made by the Zwicky Transient Facility, for the inbound leg of the comet out to a heliocentric distance ofr_h = 17 au, or approximately a year before its discovery. We find that 3I/ATLAS has been active inward of a heliocentric distance of at leastr_h = 6.5 au. The comet followed a brightening rate of $\propto r_{\mathrm{h}}^{-3.8}$ , which is significantly steeper than that of the only other known interstellar comet, 2I/Borisov, and is more consistent with dynamically old long-period comets and short-period comets in the solar system. By measuring the brightening of the dust coma, we estimate that 3I had a dust production rate of $\dot{M_{\mathrm{d}}}\sim 5\mathrm{kg}{\mathrm{s}}^{-1}$ in 2025 early May (r_h ∼ 6 au), increasing to $\dot{M_{\mathrm{d}}}\sim 30\mathrm{kg}{\mathrm{s}}^{-1}$ toward 2025 mid-July (r_h ∼ 4 au) assuming 100μm dust grains, in line with the more recent Hubble Space Telescope measurement made atr_h = 3.8 au. Comparison with the prediscovery photometry by the Transiting Exoplanet Survey Satellite suggested that 3I started producing constant dust outflow probably aroundr_h ∼ 9 au, coinciding with the turn-on distance of CO₂ice. We also conduct a deep search of 3I/ATLAS with multiple nights of data taken in 2024, when the comet was atr_h = 13–17 au, and conclude that the comet was no brighter than 2–5 mag above the coma or bare-nucleus lightcurves. This suggests that the comet did not exhibit strong outbursts during these periods, consistent with 2I/Borisov as well as most long-period solar system comets. 

Abstract 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 att_rest ≈ 50–100 days, with peak radio luminosities ranging from 10³⁸to 10⁴⁰erg s⁻¹. Modeling the radio emission as synchrotron radiation indicates a fast (v= 0.1–0.3c) shock in a dense (n_e ≈ 10³–10⁴cm⁻³) medium. The X-ray emission varies by ≈2 orders of magnitude in luminosity (10⁴²–10⁴⁴erg s⁻¹) att_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 = 10⁹–10¹¹M_⊙. 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 fromt_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. 

ABSTRACT We study AT2024kmq and AT2024lhc, two tidal disruption events (TDEs) with blue featureless spectra associated with high-mass black holes ($$M_{\rm BH}\sim 10^8\, \mathrm{ M}_\odot$$). Both events show optical precursors consistent with shock dissipation from stream self-intersection. Their X-ray emission is luminous ($$L_{\rm X}\sim 10^{44}\, {\rm erg\, s^{-1}}$$), 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 $$1.7\lt \Gamma \lt 3$$ (where $$f_\nu \propto \nu ^{1-\Gamma }$$). The X-ray properties and radio non-detections support a compact corona ($$\lesssim 10 r_{\rm g}$$) 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 $$M_{\rm BH}$$ distributions in TDEs with different X-ray spectral evolution properties: low-mass black holes ($$M_{\rm BH} \sim 10^6 \mathrm{ M}_\odot$$) remain soft ($$\Gamma \gt 4$$) within $$t\lesssim 2$$ yr, intermediate masses ($$\sim 10^7 \mathrm{ M}_\odot$$) transition from soft to hard at $$\sim$$1 yr, while high masses ($$\sim 10^8 \mathrm{ M}_\odot$$) are hard ($$1.5\lt \Gamma \lesssim 3$$) from the outset. We interpret this result as evidence that the soft-to-hard state transition in TDEs occurs at the critical threshold of $$\dot{M}_{\rm acc} \sim 0.03 \dot{M}_{\rm Edd}$$ (similar to X-ray binaries), using the fact that the transition time-scale predicted by simple disc theory scales with black hole mass as $$t_{\rm tr}\propto M_{\rm BH}^{-3/4}$$. 

Abstract Recent studies suggest that tidal disruption events (TDEs) with off-axis jets may manifest as optically overluminous events. To search for jet signatures at late times, we conducted radio observations of eight such optically overluminous (M_g,peak < −20.8 mag) TDEs with the Very Large Array. We detect radio counterparts in four events. The observed radio luminosities (L_{6 GHz} ∼ 10³⁸–10³⁹erg s⁻¹) are two orders of magnitude lower than those of on-axis jetted TDEs, and we find no evidence for off-axis jets within a rest-frame time of 3 yr. Two of them (AT2022hvp and AT2021aeou) exhibit evolving radio emission, consistent with synchrotron emission from non-relativistic outflows launched near the time of first optical light. Two events (AT2020ysg and AT2020qhs) show no statistically significant variability, which can be attributed to either non-relativistic outflows or pre-existing active galactic nuclei. Compared to a control sample of fainter TDEs withM_g,peak > −20.5 mag observed at similar rest-frame timescales (t_rest ∼ 1.5 yr), our sample shows systematically more luminous radio emission, suggesting that optically overluminous TDEs may launch more powerful prompt non-relativistic outflows. We speculate that strong general relativistic effects near high-mass black holes (M_BH ∼ 10⁸M_⊙) may play a key role. These findings motivate further investigation into the nature of relativistic disruptions around massive black holes and the physical conditions necessary for jet formation. 

Abstract We present the discovery of SN 2025wny (ZTF25abnjznp/GOTO25gqt) and spectroscopic classification of this event as the first gravitationally lensed Type I superluminous supernova (SLSN-I). Deep ground-based follow-up observations resolve four images of the supernova with $\sim 1\stackrel{″}{.}7$ angular separation from the main lens galaxy, each coincident with the lensed images of a background galaxy seen in archival imaging of the field. Spectroscopy of the brightest image shows narrow features matching absorption lines at a redshift ofz= 2.010 and broad features matching those seen in superluminous SNe with far-UV coverage. We infer a magnification factor ofμ ∼ 20–50 for the brightest image in the system, based on photometric and spectroscopic comparisons to other SLSNe-I. SN 2025wny demonstrates that gravitationally lensed SNe are in reach of ground-based facilities out to redshifts far higher than previously assumed, and provide a unique window into studying distant supernovae and the internal properties of dwarf galaxies, as well as for time-delay cosmography. 

Abstract Eruptive mass loss of massive stars prior to supernova (SN) explosion is key to understanding their evolution and end fate. An observational signature of pre-SN mass loss is the detection of an early, short-lived peak prior to the radioactive-powered peak in the lightcurve of the SN. This is usually attributed to the SN shock passing through an extended envelope or circumstellar medium. Such an early peak is common for double-peaked Type IIb SNe with an extended hydrogen envelope but uncommon for normal Type Ibc SNe with very compact progenitors. In this paper, we systematically study a sample of 14 double-peaked Type Ibc SNe out of 475 Type Ibc SNe detected by the Zwicky Transient Facility. The rate of these events is ∼3%–9% of Type Ibc SNe. A strong correlation is seen between the peak brightness of the first and the second peak. We perform a holistic analysis of this sample’s photometric and spectroscopic properties. We find that six SNe have ejecta mass less than 1.5M_⊙. Based on the nebular spectra and lightcurve properties, we estimate that the progenitor masses for these are less than ∼12M_⊙. The rest have an ejecta mass >2.4M_⊙and a higher progenitor mass. This sample suggests that the SNe with low progenitor masses undergo late-time binary mass transfer. Meanwhile, the SNe with higher progenitor masses are consistent with wave-driven mass loss or pulsation-pair instability-driven mass-loss simulations. 

Abstract The accretion disks of active galactic nuclei (AGNs) are promising locations for the merger of compact objects detected by gravitational wave (GW) observatories. Embedded within a baryon-rich, high-density environment, mergers within AGNs are the only GW channel where an electromagnetic (EM) counterpart must occur (whether detectable or not). Considering AGNs with unusual flaring activity observed by the Zwicky Transient Facility (ZTF), we describe a search for candidate EM counterparts to binary black hole (BBH) mergers detected by LIGO/Virgo in O3. After removing probable false positives, we find nine candidate counterparts to BBH mergers during O3 (seven in O3a, two in O3b) with a p -value of 0.0019. Based on ZTF sky coverage, AGN geometry, and merger geometry, we expect ≈3( N BBH /83)( f AGN /0.5) potentially detectable EM counterparts from O3, where N BBH is the total number of observed BBH mergers and f AGN is the fraction originating in AGNs. Further modeling of breakout and flaring phenomena in AGN disks is required to reduce our false-positive rate. Two of the events are also associated with mergers with total masses >100 M ⊙ , which is the expected rate for O3 if hierarchical (large-mass) mergers occur in the AGN channel. Candidate EM counterparts in future GW observing runs can be better constrained by coverage of the Southern sky as well as spectral monitoring of unusual AGN flaring events in LIGO/Virgo alert volumes. A future set of reliable AGN EM counterparts to BBH mergers will yield an independent means of measuring cosmic expansion ( H 0 ) as a function of redshift.