arXiv subjects

Erica Hammerstein

Publications and source records attributed to Erica Hammerstein.

At least 19 recordsLinked to original sources

arXiv2026

4th TDAMM Workshop White Paper

Time-Domain and Multi-Messenger Astrophysics (TDAMM) is entering a new era in which the rate and diversity of transient discoveries will grow rapidly across electromagnetic, gravitational-wave, neutrino, and cosmic-ray facilities. The scientific return from these investments will increasingly depend not on discovery alone, but on the ability to identify, prioritize, and coordinate follow-up observations across a heterogeneous and globally distributed network of observatories. This white paper summarizes the outcomes of the Fourth TDAMM Workshop and assesses the near-term discovery landscape, the infrastructure and tools that support coordinated observations, and the technical, policy, and capability gaps that may limit future progress. The workshop identified three principal challenges: insufficiently scalable and interoperable alert and coordination infrastructure, policies that impede rapid multi-facility observations and rare-event science, and the potential loss of critical high-energy, rapid-response, and spectroscopic capabilities. The white paper identifies the need for sustained support for alert distribution, brokers, standardized observatory metadata, cross-facility coordination platforms, and unified follow-up repositories; expanded joint observing opportunities and funding mechanisms for coordinated analysis; and strategic investment in future TDAMM facilities. The white paper also present a framework for community observing plans that would establish pre-coordinated responses to rare, high-impact events, supported by transparent governance, immediate public data release, and regular community revision. Science overviews and detailed observing strategies are provided for gamma-ray bursts, tidal disruption events, X-ray binaries, novae, supernovae, magnetars, compact binary mergers, and high-energy neutrino sources.

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arXiv2026

Late-time JWST/NIRCam Observations of the Extremely Long-duration GRB 250702B/EP 250702a and Its Host Galaxy

We present JWST/NIRCam observations of the extremely long-duration gamma-ray burst (GRB) 250702B taken at ~ 95 days post-GRB (observer frame). The observations of the host galaxy reveal a single galaxy with a prominent dust lane observed nearly edge-on. Prospector modeling of the host galaxy photometry finds a high stellar mass (log(M_*/M_Sun) = 11.0 +0.2/-0.3) and large dust column (A_V = 2.8 +/- 0.3 mag), in agreement with previous results. If GRB 250702B is a collapsar-driven GRB, the host galaxy is the brightest (in rest-frame r and rest-frame H) and most massive compared to GRB hosts at similar redshifts. The transient localization is near the dust lane, and while we find no evidence for transient emission in F277W, F356W, and F444W, forced photometry in F150W and F200W reveals possible ~ 3 sigma detections of the transient at m_{F150W} ~ 27.9 AB mag and m_{F200W} ~ 27.4 AB mag. If these are secure detections, they are indicative of a late-time light curve flattening. This behavior is consistent with that of jetted tidal disruption events (TDEs); however, it is also consistent with a supernova plus GRB afterglow model. Alternatively, if these are upper limits, they are consistent with, but do not further constrain, the extrapolated power-law decline of the afterglow. The ambiguity of the possible detection of the transient in F150W and F200W highlights the need for late-time template observations with JWST/NIRCam.

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arXiv2026

Discovery of a Featureless Tidal Disruption Event at z~1 with the Wide Field Survey Telescope

We report the discovery of tidal disruption event (TDE) WFST250820mmsw/AT2025wet by the 2.5-meter Wide Field Survey Telescope (WFST). It exhibits a blue nuclear flare throughout the observed evolution with a g-band peak magnitude ~22, which is about 3 magnitudes brighter than its host galaxy. A Keck/LRIS spectrum taken near the optical peak reveals a featureless blue continuum, with no discernible emission lines. However, its redshift can be accurately determined to be 1.037 by its host galaxy absorption lines. Blackbody fits to the multiband spectral energy distribution (SED) of AT2025wet yield a constant temperature of ~19,000K and a peak luminosity of (8.27 +0.92 -0.71)*10^44 erg s^-1 while actually the SED likely peaks at a much shorter wavelength than a 19,000K blackbody. The SED modeling of the host galaxy implies a stellar mass of ~10^11.2 M_odot and an estimated central black hole mass of ~10^8 M_odot, with no evidence of significant active galactic nucleus activity prior to the flare. All of these observations are well consistent with a featureless TDE scenario, making it the highest-redshift non-jetted TDE known to date. TDEs at such high redshift provide us a unique opportunity to explore the intrinsic SEDs of TDEs, particularly to test whether they peak in the extreme-UV regime, thereby addressing the missing energy puzzle and the origin of optical emission in TDEs. Ongoing surveys represented by WFST and the Legacy Survey of Space and Time (LSST) are expected to discover an increasing number of TDEs at higher redshifts, which will extend our census of SMBHs across redshift space and help unravel the mysteries of optical TDEs through direct probes of their UV emission.

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arXiv2026

A 14-year-old Mystery: The Peculiar Case of the Engine-driven SN 2012ap

We present late-time ($\delta t > 3000$ d) optical (Keck), X-ray (Chandra and NuSTAR), and radio (VLA, ALMA, and the uGMRT) observations of the Type Ic-BL SN 2012ap. Previous studies of this SN suggested that it stands out as a key example of a weak engine-driven explosion due to the lack of gamma-ray burst detection and a mildly relativistic ejecta. Recently, radio sky surveys revealed the rebrightening of the radio emission from this SN, highlighting the possibilities of a density enhancement at large radii or the existence of an off-axis relativistic jet. While the late-time optical spectra does not exhibit the broad emission lines seen in other interacting SNe, our analysis of the broadband radio and X-ray emission implies that both scenarios are plausible. If a density enhancement is responsible for the radio rebrightening, it has to result from a change in the mass-loss rate and/or wind velocity, possibly due to the transition of the progenitor from a red supergiant to a Wolf-Rayet star. If the late-time radio component is a result of an off-axis relativistic jet, we find that an energetic narrow jet viewed at $\theta_{\rm obs} \geq 80^{\circ}$ is needed. In this scenario, SN 2012ap is not a result of a weak engine-driven explosion, and, instead, it is similar to other GRBs. However, radio rebrightenings of Type Ic-BL SNe are not enough on their own to determine the existence of off-axis jets and our planned VLBA observation will help reveal the true nature of this SN.

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arXiv2026

UGC 2369S: a Kpc Scale Triple Merger Candidate Identified in a Nearby Luminous Infrared Galaxy

We present high spatial resolution ($\lesssim$1.0''), multi-wavelength observations of UGC 2369S, a nearby luminous infrared galaxy showing three distinct cores separated on kpc scales in near-infrared (NIR) imaging with significant X-ray emission. Utilizing optical/NIR adaptive optics (AO), radio, \chandra X-ray, as well as archival HST imaging, we perform a comprehensive study of AGN activity, obscuration, and host properties. As one of the clearest cases of a triple-nucleus merger at $\simeq$3 kpc separations, UGC 2369S is the first to be studied with high-resolution observations at multiple wavelength. We find that the northern core, having possibly the most massive black hole in the system ($\rm M_{BH}\simeq10^{8}\,M_{\odot}$) is consistent with a heavily obscured AGN. However, its high dust extinction ($\rm A_v>5$), hydrogen column density ($N_\mathrm{H}\gtrsim 10^{25}\,\rm cm^{-2}$) and non-detection of optical coronal lines and coronal X-ray emission leave the identification inconclusive. The other two cores show no evidence for black-hole activity and instead exhibit signatures of tidal disruption. From stellar mass surface density and stellar velocity dispersion maps, we infer that the strongly varying gravitational potential in this three-body system may have cannibalized the stellar bulge of the southwestern core, leaving a metal enriched remnant. An ongoing survey focusing on similar triple systems could help us understand how they evolve and help benchmark numerical simulations, providing insight into gravitational wave predictions and the formation of the most massive black holes.

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arXiv2026

AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events

We study AT2024kmq and AT2024lhc, two tidal disruption events (TDEs) with blue featureless spectra associated with high-mass black holes ($M_{\rm BH}\sim 10^8\,M_\odot$). 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 timescales of 1.3\,hr and 4.8\,hr for factor of $\sim3$ flux changes), long-lasting ($>1\,\rm yr$), emerging no later than the optical peak, and well characterized by power-laws with $1.7<\Gamma<3$ (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 UV/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 ($M_{\rm BH} \sim 10^6 M_\odot$) remain soft ($\Gamma>4$) within $t\lesssim 2$\,yr, intermediate masses ($\sim 10^7 M_\odot$) transition from soft to hard at $\sim$1 yr, while high masses ($\sim 10^8 M_\odot$) are hard ($1.5<\Gamma\lesssim 3$) 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 timescale predicted by simple disk theory scales with black hole mass as $t_{\rm tr}\propto M_{\rm BH}^{-3/4}$.

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arXiv2026

TDE 2025abcr: A Tidal Disruption Event in the Outskirts of a Massive Galaxy

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 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 ML classifier $\texttt{tdescore}$, which classifies new ZTF transients based on their lightcurves. Follow-up observations confirm that TDE 2025abcr is a TDE-H+He, occurring 9.5$"$ (9.3 kpc projected distance) from the nucleus of a massive galaxy ($\mathrm{M}_{\star}$ = $10^{11.18 \pm 0.03}\mathrm{M}_{\odot}$) with a central black hole mass of $10^{8.82 \pm 0.65}\mathrm{M}_{\odot}$. TDE 2025abcr itself was likely disrupted by a much lighter black hole ($10^{6.09\pm0.53}\mathrm{M}_{\odot}$, as estimated with peak luminosity scaling relations). The black hole 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' black hole. The rate of highly offset ($\gtrsim$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 each year with resolvable offsets.

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arXiv2026

The DESI Transients Survey: Legacy Classifications and Methodology

We present the first systematic spectroscopic observations of extragalactic transients from the Dark Energy Spectroscopic Instrument (DESI), as part of the DESI Transients Survey program. With 5,000 fibers and an ${\sim} 8$ deg$^2$ field of view, we exploit DESI as a machine for the discovery and classification of transients. We present transient classifications from archival DESI data in Data Releases 1 and 2, relying on a combination of a secondary target program and serendipitous observations. We also present observations from the first 6 months of the DESI spare fiber program dedicated to transients. The program is run in coordination with a dedicated DECam time-domain survey, serving as a pathfinder for what we will be able to achieve in conjunction with the Rubin Observatory Legacy Survey of Space and Time (LSST). We classify over 250 transients, of which the majority were previously unclassified. The sample comprises thermonuclear and core-collapse supernovae and tidal disruption events (TDEs), including a TDE observed before its discovery in imaging. We demonstrate DESI's ability to classify a population of faint transients down to $r\sim 22.5$ mag during main survey operations, with negligible impacts on DESI's main observations.

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arXiv2025

Tidal Disruption Events

Stars that orbit too close to a black hole can be ripped apart by strong tides, producing a type of luminous transient event called a ``tidal disruption event" (TDE). Tidal disruption events of stars by supermassive black holes (SMBHs) provide windows into the nuclei of galaxies at size scales that are difficult to observe directly outside our own galactic neighborhood. They provide a unique opportunity to study these supermassive black holes under feeding conditions that change dramatically over ~week-month timescales, and that regularly reach super-Eddington mass inflow rates. Their light curves are dependent on the properties of the disrupting black hole, and can be used to help constrain the lower mass end of the SMBH mass function -- a region of parameter space that is difficult to access with classic dynamical mass measurements.

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arXiv2025

Ultraviolet Spectral Evidence for Ansky as a Slowly Evolving Featureless Tidal Disruption Event with Quasiperiodic Eruptions

X-ray quasi-periodic eruptions (QPEs) are rare and enigmatic phenomena that increasingly show a connection to tidal disruption events (TDEs). However, the recently discovered QPEs in ZTF19acnskyy ("Ansky") appear to be linked to an active galactic nucleus (AGN) rather than a TDE, as their slow decay and AGN-like variability differ markedly from that of typical TDEs. This finding may imply broader formation channels for QPEs. To further investigate Ansky's nature, we obtained a timely ultraviolet (UV) spectrum, which reveals a featureless, TDE-like spectrum devoid of broad optical or UV emission lines. Additionally, the steep UV continuum, fitted by a power law with an index of -2.6, aligns more closely with TDEs than with AGNs. Compared to other featureless TDEs, Ansky exhibits a significantly lower blackbody luminosity (10^43 erg s^-1) and much longer rise and decay timescales, suggesting a distinct TDE subclass. An offset TDE involving an intermediate-mass black hole is unlikely, given its position consistent with the galactic center with a 3 sigma upper limit of 54 pc. Instead, we propose that Ansky may result from the tidal disruption of a post-main-sequence star by a typical supermassive black hole. Our findings strengthen the growing evidence for TDE-QPE associations, although other formation channels for QPEs remain plausible and await future observational efforts.

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arXiv2025

The Most Luminous Known Fast Blue Optical Transient AT 2024wpp: Unprecedented Evolution and Properties in the Ultraviolet to the Near-Infrared

We present an extensive photometric and spectroscopic ultraviolet-optical-infrared campaign on the luminous fast blue optical transient (LFBOT) AT 2024wpp over the first ~100 d. AT 2024wpp is the most luminous LFBOT discovered to date, with $L_{\rm{pk}}\approx(2-4)\times10^{45}$ erg s$^{-1}$ (5-10 times that of the prototypical AT 2018cow). This extreme luminosity enabled the acquisition of the most detailed LFBOT UV light curve thus far. In the first ~45 d, AT 2024wpp radiated $>10^{51}$ erg, surpassing AT 2018cow by an order of magnitude and requiring a power source beyond the radioactive $^{56}$Ni decay of traditional supernovae. Like AT 2018cow, the UV-optical spectrum of AT 2024wpp is dominated by a persistently blue thermal continuum throughout our monitoring, with blackbody parameters at peak of T>30,000 K and $R_{\rm{BB}}/t\approx0.2-0.3c$. A temperature of $\gtrsim$20,000 K is maintained thereafter without evidence for cooling. We interpret the featureless spectra as a consequence of continuous energy injection from a central source of high-energy emission which maintains high ejecta ionization. After 35 d, faint (equivalent width <10 {\AA}) H and He spectral features with kinematically separate velocity components centered at 0 km s$^{-1}$ and -6400 km s$^{-1}$ emerge, implying spherical symmetry deviations. A near-infrared excess of emission above the optical blackbody emerges between 20-30 d with a power-law spectrum $F_{\rm\nu,NIR}\propto\nu^{-0.3}$ at 30 d. We interpret this distinct emission component as either reprocessing of early UV emission in a dust echo or free-free emission in an extended medium above the optical photosphere. LFBOT asphericity and multiple outflow components (including mildly relativistic ejecta) together with the large radiated energy are naturally realized by super-Eddington accretion disks around neutron stars or black holes and their outflows.

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arXiv2025

The First Radio-Bright Off-Nuclear TDE 2024tvd Reveals the Fastest-Evolving Double-Peaked Radio Emission

We present the first multi-epoch broadband radio and millimeter monitoring of an off-nuclear TDE using the VLA, ALMA, ATA, AMI-LA, and the SMA. The off-nuclear TDE 2024tvd exhibits double-peaked radio light curves and the fastest evolving radio emission observed from a TDE to date. With respect to the optical discovery date, the first radio flare rises faster than $F_{\rm \nu} \sim t^{9}$ at $\Delta t = 88-131$ days, and then decays as fast as $F_{\rm \nu} \sim t^{-6}$. The emergence of a second radio flare is observed at $\Delta t \approx 194$ days with an initial fast rise of $F_{\rm \nu} \sim t^{18}$, and an optically thin decline of $F_{\rm \nu} \sim t ^{-12}$. We interpret these observations in the context of a self-absorbed and free-free absorbed synchrotron spectrum, while accounting for both synchrotron and external inverse-Compton cooling. We find that a single prompt outflow cannot easily explain these observations and it is likely that either there is only one outflow that was launched at $\Delta t \sim 80$ days, or two distinct outflows, with the second launched at $\Delta t \sim 170-190$ days. The nature of these outflows, whether sub-, mildly-, or ultra-relativistic, is still unclear, and we explore these different scenarios. Finally, we find a temporal coincidence between the launch time of the first radio-emitting outflow and the onset of a power-law component in the X-ray spectrum, attributed to inverse-Compton scattering of thermal photons.

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arXiv2025

Optically Overluminous Tidal Disruption Events: Outflow Properties and Implications for Extremely Relativistic Disruptions

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 ($M_{g, \rm peak} < -20.8$ mag) TDEs with the Very Large Array. We detect radio counterparts in four events. The observed radio luminosities ($L_{\rm 6 GHz} \sim 10^{38}$--$10^{39}$ erg 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 rest-frame time of 3 yrs. 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 with $M_{g, \rm peak} > -20.5$ mag observed at similar rest-frame timescales ($t_{\rm rest} ~ 1.5$\,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 ($M_{\rm BH} ~ 10^8\,M_\odot$) 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.

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arXiv2025

The Jetted Tidal Disruption Event AT2022cmc: Investigating Connections to the Optical Tidal Disruption Event Population and Spectral Subclasses Through Late-Time Follow-up

AT2022cmc is the first on-axis jetted tidal disruption event (TDE) to be discovered at optical wavelengths. The optically bright nature of AT2022cmc presents an unprecedented opportunity to place this jetted TDE in the context of the larger optically selected thermal TDE population and explore potential connections to optical TDE subclasses, particularly the class of luminous TDEs that lack optical spectral features. In this work we present late-time optical observations of AT2022cmc, both imaging and spectroscopy, that extend the optical dataset to $\sim 160$ days from the first detection in the observed frame. The light curve clearly evolves from red to blue, which we interpret as a transition from a non-thermally dominated spectral energy distribution (SED) to thermally dominated SED. By accounting for the non-thermal emission evident in the optical SED at early times, we extract the properties of the thermal emission and compare to a sample of optically selected thermal TDEs. We find that the properties of AT2022cmc are consistent with previous correlations found for the evolution and properties of thermal TDEs, with the thermal properties of AT2022cmc aligning with the class of featureless and luminous TDEs. The confirmation of this similarity motivates the importance of prompt and multi-wavelength follow-up of featureless and luminous TDEs in order to further explore the connection they have with jetted TDEs.

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arXiv2025

A luminous and hot infrared through X-ray transient at a 5 kpc offset from a dwarf galaxy

We are searching for hot, constant-color, offset optical flares in the Zwicky Transient Facility (ZTF) data stream that are ${>}10''$ from any galaxy in public imaging data from the PanSTARRS survey. Here, we present the first discovery from this search: AT 2024puz, a luminous multiwavelength transient offset by $5\,$kpc from a ${\sim}10^8\,M_\odot$ galaxy at $z=0.356$ with a low-moderate star formation rate. It produced luminous $10^{44.79 \pm 0.04}\,{\rm erg\,s}^{-1}$ optical/UV emission that evolved on a ${\sim}20\,$day timescale, as well as $10^{44.12\pm0.03}\,{\rm erg\,s}^{-1}$ X-ray emission with a photon-index $\Gamma=1.7$. No associated radio or millimeter emission was detected. We show that the early-time optical emission is likely powered by reprocessing of high-energy, accretion-powered radiation, with a possible contribution from a shock in a dense circum-transient medium. If the shock is dominant at early-times, the circum-transient medium has a mass ${\sim}0.1-1\,M_\odot$, radius $10^{15}\,$cm, and a density profile shallower than ${\sim}r^{-1}$. A near-infrared excess appears at late-times and is suggestive of reprocessing within a wind or other circum-transient medium. The X-rays are most consistent with a central engine. We suggest that AT 2024puz may be associated with an accretion event onto a $50-10^5\,M_\odot$ BH, where the lower masses are preferred based on the large projected offset from the host galaxy. AT2024puz exhibits properties similar to both luminous fast blue optical transients (LFBOTs) and tidal disruption events (TDEs), but is intermediate between them in its energetics and evolution timescale. This highlights the need for broader exploration of the landscape of hot optical transients to trace their origins.

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arXiv2025

The La Silla Schmidt Southern Survey

We present the La Silla Schmidt Southern Survey (LS4), a new wide-field, time-domain survey to be conducted with the 1 m ESO Schmidt telescope. The 268 megapixel LS4 camera mosaics 32 2k$\times$4k fully depleted CCDs, providing a $\sim$20 deg$^2$ field of view with $1''$ pixel$^{-1}$ resolution. The LS4 camera will have excellent performance at longer wavelengths: in a standard 45 s exposure the expected 5$\sigma$ limiting magnitudes in $g$, $i$, $z$ are $\sim$21.5, $\sim$20.9, and $\sim$20.3 mag (AB), respectively. The telescope design requires a novel filter holder that fixes different bandpasses over each quadrant of the detector. Two quadrants will have $i$ band, while the other two will be $g$ and $z$ band and color information will be obtained by dithering targets across the different quadrants. The majority (90%) of the observing time will be used to conduct a public survey that monitors the extragalactic sky at both moderate (3 d) and high (1 d) cadence, as well as focused observations within the Galactic bulge and plane. Alerts from the public survey will be broadcast to the community via established alert brokers. LS4 will run concurrently with the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST). The combination of LS4+LSST will enable detailed holistic monitoring of many nearby transients: high-cadence LS4 observations will resolve the initial rise and peak of the light curve while less-frequent but deeper observations by LSST will characterize the years before and after explosion. Here, we summarize the primary science objectives of LS4 including microlensing events in the Galaxy, extragalactic transients, the search for electromagnetic counterparts to multi-messenger events, and cosmology.

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arXiv2025

Low-Luminosity Type IIP Supernovae from the Zwicky Transient Facility Census of the Local Universe. I: Luminosity Function, Volumetric Rate

We present the luminosity function and volumetric rate of a sample of Type IIP supernovae (SNe) from the Zwicky Transient Facility Census of the Local Universe survey (CLU). This is the largest sample of Type IIP SNe from a systematic volume-limited survey to-date. The final sample includes 330 Type IIP SNe and 36 low-luminosity Type II (LLIIP) SNe with $M_{\textrm{r,peak}}>-16$ mag, which triples the literature sample of LLIIP SNe. The fraction of LLIIP SNe is $19^{+3}_{-4}\%$ of the total CLU Type IIP SNe population ($8^{+1}_{-2}\%$ of all core-collapse SNe). This implies that while LLIIP SNe likely represent the fate of core-collapse SNe of $8-12$ \Msun\ progenitors, they alone cannot account for the fate of all massive stars in this mass range. To derive an absolute rate, we estimate the ZTF pipeline efficiency as a function of the apparent magnitude and the local surface brightness. We derive a volumetric rate of $(3.9_{-0.4}^{+0.4}) \times 10^{4}\ \textrm{Gpc}^{-3}\ \textrm{yr}^{-1}$ for Type IIP SNe and $(7.3_{-0.6}^{+0.6}) \times 10^{3}\ \textrm{Gpc}^{-3}\ \textrm{yr}^{-1}$ for LLIIP SNe. Now that the rate of LLIIP SNe is robustly derived, the unresolved discrepancy between core-collapse SN rates and star-formation rates cannot be explained by LLIIP SNe alone.

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arXiv2025

A Massive Black Hole 0.8 kpc from the Host Nucleus Revealed by the Offset Tidal Disruption Event AT2024tvd

Tidal disruption events (TDEs) that are spatially offset from the nuclei of their host galaxies offer a new probe of massive black hole (MBH) wanderers, binaries, triples, and recoiling MBHs. Here we present AT2024tvd, the first off-nuclear TDE identified through optical sky surveys. High-resolution imaging with the \textit{Hubble Space Telescope} shows that AT2024tvd is $0.914\pm 0.010^{\prime\prime}$ offset from the apparent center of its host galaxy, corresponding to a projected distance of $0.808\pm 0.009$ kpc at $z=0.045$. Chandra and VLA observations support the same conclusion for the TDE's X-ray and radio emission. AT2024tvd exhibits typical properties of nuclear TDEs, including a persistent hot UV/optical component that peaks at $L_{\rm bb}\sim 6\times 10^{43}\,{\rm erg\,s^{-1}}$, broad hydrogen lines in its optical spectra, and delayed brightening of luminous ($L_{\rm X,peak}\sim 3\times 10^{43}\,{\rm erg\,s^{-1}}$), highly variable soft X-ray emission. The MBH mass of AT2024tvd is $10^{6\pm1}\,M_\odot$, at least 10 times lower than its host galaxy's central black hole mass ($\gtrsim 10^8\,M_\odot$). The MBH in AT2024tvd has two possible origins: a wandering MBH from the lower-mass galaxy in a minor merger during the dynamical friction phase or a recoiling MBH ejected by triple interactions. Combining AT2024tvd with two previously known off-nuclear TDEs discovered in X-rays (3XMM J2150 and EP240222a), which likely involve intermediate-mass black holes in satellite galaxies, we find that the parent galaxies of all three events are very massive ($\sim 10^{10.9}\,M_\odot$). This result aligns with expectations from cosmological simulations that the number of offset MBHs scales linearly with the host halo mass.

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