arXiv subjects

Sam Rose

Publications and source records attributed to Sam Rose.

At least 19 recordsLinked to original sources

arXiv2026

Infrared spectroscopy of the longest-period Galactic Mira variables from Palomar Gattini-IR: Identification of a candidate thermally pulsing Super-Asymptotic Giant Branch star

The population of extremely long-period Mira variables in the Milky Way remains poorly characterized. Their rarity and heavy circumstellar obscuration have precluded systematic studies in optical surveys, yet they are expected to trace the most massive stars evolving through the Asymptotic Giant Branch (AGB). We present IRTF/SpeX spectroscopy of the longest-period ($P\gtrsim1000$ d) Galactic Mira variables identified with the Palomar Gattini-IR survey. Twelve of thirteen targets exhibit characteristics consistent with massive O-rich AGB stars. In contrast, one peculiar source IRAS 19552+3142 exhibits i) a large-amplitude ($ΔJ\gtrsim2$ mag) pulsations with $P\approx1060$ d, ii) strong C$_2$ and CO molecular bands indicating C/O$\gtrsim1$, and iii) SiC emission at $\approx11.3\,μ$m in archival mid-infrared spectra. Its spectroscopically confirmed chemistry makes it the longest period C-rich Galactic Mira variable known; together with the rarity of similar objects, this source is difficult to reconcile with standard massive AGB evolution where hot-bottom burning maintains an O-rich surface composition. Instead, its properties may be explained by super-AGB evolution where dredge-out episodes produce a C-rich surface and circumstellar material. Its high luminosity ($M_{[4.5]}\lesssim-10$ mag), red color ($[3.6] - [4.5]\gtrsim2.0$ mag), and high mass-loss rate ($\gtrsim 10^{-4} \mathrm{M_\odot yr^{-1}}$) resemble extreme AGB star progenitors of intermediate-luminosity red transients in nearby galaxies and a known chemically peculiar super-AGB star candidate in the Small Magellanic Cloud. IRAS 19552+3142 may thus provide a rare look at a Galactic super-AGB star in the thermally pulsing phase. Our results motivate improved theoretical predictions and long-baseline infrared searches for these short-lived, dust-enshrouded endpoints of stellar evolution.

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arXiv2026

SN 2025wiu: A Type Ib Supernova with Post-Peak Optical Rebrightening

We present optical photometric and optical/near-infrared spectroscopic observations of SN 2025wiu, a Type Ib supernova (SN) at z = 0.046927. The r-band light curve exhibits an initial maximum of approximately -18.2 mag, followed by a weaker optical rebrightening reaching approximately -17.8 mag at +38 days in the rest frame relative to the first maximum. However, the reconstructed bolometric light curve does not show a distinct second peak, but instead exhibits a reduced decline rate during the corresponding phase. The spectra consistently show Type Ib features without narrow emission components associated with circumstellar material. The late-time bolometric decline rate of 0.054 +/- 0.008 mag/day is faster than expected for complete trapping of 56Co decay. A radioactive-decay model for the first peak requires nickel mass = 0.47 solar masses, above the range typical of SNe Ib. A combined radioactive-decay and circumstellar-interaction model reproduces the full bolometric light curve with nickel mass ~ 0.38 solar masses, ejecta mass ~ 4.7 solar masses, and an effective circumstellar mass of ~ 0.10 solar masses, with the interaction contributing from the first peak onward. The lack of interaction signatures in the spectra favours an aspherical, disk-like circumstellar structure engulfed by the ejecta, in which the interaction energy is thermalized below the ejecta photosphere; the fitted circumstellar parameters are therefore effective values rather than direct measurements of the circumstellar geometry. SN 2025wiu demonstrates that optical rebrightening does not necessarily imply a genuine bolometric secondary maximum and highlights the importance of multi-band observations for identifying the powering mechanisms of double-peaked stripped-envelope supernovae.

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arXiv2026

First Pre-peak Ultraviolet Spectrum of a Tidal Disruption Event: A Fast Outflow Revealed Prior to Maximum Light in TDE2025aarm

The tidal disruption and eventual accretion of a star by a massive black hole can lead to the launching of outflows and winds that encode important information about the tidal disruption and accretion processes. However, little is known about the existence and behavior of these outflows before optical light-curve peak, when processes such as stream-stream collisions and disk formation may be important. Here, we present the first pre-peak ultraviolet (UV) spectrum of a tidal disruption event (TDE), obtained $\sim 20$ days before optical maximum light of the nearby (redshift $z=0.0137$) TDE2025aarm, along with quasi-simultaneous infrared (IR) through X-ray observations. Our HST/STIS spectrum shows strong evidence for an early-time outflow through broad near-UV (NUV) and far-UV (FUV) absorption lines blueshifted by $\sim$10,000 km s$^{-1}$, including two new UV broad absorption features not yet identified in a TDE. We find that the FUV--IR continuum deviates significantly from a blackbody ($f_λ\propto λ^{-3.08}$), which we interpret as a signature of reprocessing through the outflow. This deviation implies that the bolometric luminosity in optical TDEs may be underestimated by a significant factor ($\sim$9 in this case) when inferred from single-temperature blackbody fits to NUV--optical photometry alone. This work further confirms that TDEs are capable of launching fast outflows at very early times and emphasizes the importance of prompt FUV spectroscopic observations of TDEs that can capture the full continuum emission and energetics.

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arXiv2026

AppleCiDEr. II. SpectraNet: A Spectroscopic Neural Network Classifier for Transients Demonstrated on ZTF Follow-up Data

Time-domain surveys such as the Zwicky Transient Facility have opened a new frontier in the discovery and characterization of transients. While photometric light curves provide broad temporal coverage, spectroscopic observations remain crucial for physical interpretation and source classification. However, existing spectral analysis methods, often reliant on template fitting or parametric models, are limited in their ability to capture the complex and evolving spectra characteristic of such sources, which are sometimes only available at low resolution. In this work, we introduce SpectraNet, a deep convolutional neural network designed to learn robust representations of optical spectra from transients. Our model combines multi-scale convolution kernels and pooling operations to extract features from preprocessed spectra in a hierarchical and interpretable manner. We train and validate SpectraNet on low-resolution time-series spectra obtained from the Spectral Energy Distribution Machine and other instruments, demonstrating better performance in classification compared to other known pipelines.

astro-ph.IM↗

arXiv2026

A data processing pipeline for the WINTER near-infrared surveyor using the $\texttt{mirar}$ framework

We present the data reduction and transient detection pipeline for the Wide-field Infrared Transient Explorer (WINTER) surveyor and report its on-sky performance. The WINTER camera utilizes cost-effective InGaAs sensors as alternatives to traditional IR sensors, and is mounted on a dedicated 1-m robotic telescope at Palomar Observatory. The WINTER camera has six detectors producing a combined field-of-view of 1.2 sq. deg. equipped with y, J, and shortened-H bands. WINTER saw first light in June 2023 and has been operating robotically since. The WINTER data processing pipeline ($\texttt{winterdrp}$) has been implemented within the broader framework $\texttt{mirar}$: a modular, open-source $\texttt{python}$ package developed for realtime processing of images from time-domain surveys. $\texttt{winterdrp}$ performs end-to-end data processing implementing data reduction and image subtraction to go from raw dithered WINTER images to transient alerts in the $\texttt{avro}$ format, which are then sent to $\texttt{SkyPortal}$ for vetting and follow-up. During a year of observations in 2024, WINTER achieved J-band median 5-$σ$ depths ranging from $18.1-18.8$ mag (AB) on its six detectors in 960 second integrations as part of its survey, with an astrometric accuracy of $\approx0.2$ arcsec (a fifth of a pixel) and a detector-performance limited photometric accuracy ranging from $\approx0.09-0.18$ mag for its six detectors. We present early science results from WINTER, which include the identification of a stellar merger in M31, dust-enshrouded outbursting young stellar objects and classical novae in the Galactic plane, NIR followup of known supernovae, and multi-messenger follow-up of neutrinos, gravitational waves, fast X-ray transients and gamma-ray bursts.

astro-ph.IM↗

arXiv2026

SPIRITS 19q: Dust Production by a Subsolar-metallicity Carbon-rich Wolf-Rayet Star in NGC 2403

We present JWST/NIRSpec IFU observations of SPIRITS 19q, the highly dust-producing carbon-rich (WC) binary candidate located in a subsolar-metallicity region of the nearby spiral galaxy NGC 2403. The observations, taken in April of 2024, confirm the association of a dusty outburst observed in 2019 by the Spitzer Space Telescope with an early-type WC star. Using models from the Potsdam Wolf-Rayet (PoWR) LMC model grid we find that the WC star of SPIRITS 19q likely has an especially high mass-loss rate ($\gtrsim$ 10$^{-4}$ $M_{\odot}$ yr$^{-1}$). From the flux peak of the IR transient as measured by Spitzer/IRAC as well as constraints on dust composition and size from the JWST spectrum, we estimate a total dust mass formed in the outburst of 6.6 $\pm$ 0.4 $\times$ 10$^{-6}$ $M_{\odot}$. Assuming a minimum orbital period of 12 years, this corresponds to a period-averaged dust production rate of $\lesssim$ 5.5 $\times$ 10$^{-7}$ $M_{\odot}$ yr$^{-1}$. These observations suggest that even a single WC system can contribute to the dust budget at subsolar metallicities, and that such systems are an important source of carbonaceous dust grains in the early universe.

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arXiv2026

Follow-up of SN 2025wny II: Superluminous Supernova Physics at Cosmic Noon

SN 2025wny is a gravitationally lensed, hydrogen-poor superluminous supernova (SLSN-I) at z = 2.015. To date, it is the most extensively observed high-redshift core-collapse SN and has the most detailed rest-frame UV observations of any SLSN. We present densely sampled rest-frame UV-to-optical photometry and spectroscopy out to +80 d post-peak (rest frame) from several facilities, including JWST, Keck, VLT, Gemini, the Palomar 200-inch, the Fraunhofer Telescope at Wendelstein, and the Liverpool Telescope. Correcting for lensing magnification, SN 2025wny reaches a peak pseudo-bolometric luminosity of $L_{\rm peak}\gtrsim4\times10^{44}$ erg s$^{-1}$ over rest-frame 1500-4230 Å, placing it within the luminosity range of typical SLSNe-I. SN 2025wny exhibits several unusual features, including a continuum excess and sharp spectral features in the FUV from +20-60 d that coincide with an FUV light-curve plateau and higher inferred blackbody temperatures. SN 2025wny's spectra also show little to no UV line blanketing, no obvious O II absorption despite high temperatures, and evidence for C II, H$α$, and possible He I. Light-curve modeling suggests that SN 2025wny may require a hybrid or non-standard power source. This work provides some of the first detailed constraints on high-redshift SLSNe and establishes SN 2025wny as an essential spectral and photometric reference for identifying and interpreting high-redshift SLSNe discovered by Rubin and Roman.

astro-ph.CO↗

arXiv2026

Multiwavelength Analysis of Six Luminous Fast Blue Optical Transients

We present multiwavelength observations and analysis of six luminous fast blue optical transients (LFBOTs) discovered in Zwicky Transient Facility (ZTF) survey data. We identified these LFBOTs from their fast light-curve evolution ($t_{1/2}\leq 12 $d), blue colors at peak brightness ($g-r\leq-0.5 $mag), a visible host galaxy, high optical luminosity ($M_g<-20$), and an X-ray or radio detection. With the exception of AT2024aehp (ZTF24abygbss), these transients exhibit peaks in their $10\,$GHz radio light curves at $t_{\text{rest}} \approx 50-100$ d, with peak radio luminosities ranging from $10^{38}-10^{40}$ erg s$^{-1}$. Modeling the radio emission as synchrotron radiation indicates a fast ($v=0.1-0.3c$) shock in a dense ($n_e\approx10^{3}-10^{4}$ cm$^{-3}$) medium. The X-ray emission varies by $\approx2$ orders of magnitude in luminosity ($10^{42}-10^{44}$ erg s$^{-1}$) at $t_{\text{rest}}\sim20 $d. Analysis of the host-galaxy photometry and spectroscopy for each transient shows that they are predominantly nonnuclear (a few kpc offset) with star-forming host galaxies of stellar masses $10^{9}-10^{11} ,M_\odot$. Unlike all other LFBOTs to date, AT2024aehp exhibited a luminous ($M<-19 $mag) plateau in the optical light curve; spectra during this plateau phase showed a featureless blue continuum. The $6-15$ GHz radio emission of AT2024aehp brightened by over an order of magnitude from $t_{\text{rest}} \approx70 $d to $t_{\mathrm{rest}} \approx130 $d. The mostly consistent radio behavior between optically selected 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, such as a massive star merging with a compact object.

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arXiv2026

An infrared echo from a circumstellar disk in the hydrogen- and helium-poor SN 2024aecx

We present near-infrared (NIR) spectroscopy of the hydrogen- and helium-poor (Type Ic) supernova (SN) 2024aecx, which displays a strong NIR excess emerging 32 days post peak. SN 2024aecx is a peculiar SN Ic that exhibited luminous shock-cooling emission at early times, suggestive of close-in circumstellar medium (CSM), unexpected for this class of SNe. Its early NIR spectra are typical for a SN Ic but with strong C I absorption features. By $\sim$32 days post peak, the spectra show a strong NIR excess, while maintaining normal optical colors, unprecedented for SNe Ic. We find that the NIR excess is well fit with a single-temperature, optically thin dust model with declining temperature, increasing mass, and roughly constant luminosity over time. The NIR excess appears too promptly for dust to have formed in the SN ejecta, indicating an IR echo from pre-existing dust in the CSM. The IR echo is likely powered by the relatively slowly evolving SN peak light, and not the brief shock cooling emission, as the latter requires unrealistically high CSM densities to explain the observed dust mass. We consider different potential CSM geometries and find that a thick face-on disk with an inner edge of around $5\times 10^{16} \rm \ cm$ can best explain the dust mass and temperature evolution. In this scenario, the SN shock should start interacting with this CSM $440\pm200$ days post explosion. CSM around SN Ic is rare, and follow-up observations of SN 2024aecx will probe the mass-loss process responsible for removing hydrogen and helium from their progenitor star.

astro-ph.HE↗

arXiv2026

EP250827b/SN 2025wkm: An X-ray Flash-Supernova Powered by a Central Engine and Circumstellar Interaction

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 $\sim 10^{45} \, \rm{erg \, s^{-1}}$, lasts over 1000 seconds, and has a peak energy $E_{\rm{p}} < 1.5$ keV at 90\% confidence. SN 2025wkm possesses a double-peaked optical light curve (LC), though its bolometric luminosity plateaus after its initial peak for $\sim 20$ 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 $\gtrsim 10^{50}~$erg assuming a typical LGRB circumburst constant density ($n \approx 10^{-3}$--$10^{-1}~{\rm cm}^{-3}$) and microphysical parameters ($ε_{\rm e} = 0.1$ and $ε_{\rm B} = 0.01$). 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 $\sim 0.35c$ and interact with an extended circumstellar medium with radius $\sim 10^{13}$ cm, generating X-ray breakout emission through non-thermal 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 powers the late-time emission. We end by discussing the landscape of XRF-SNe within the context of EP's recent discoveries.

astro-ph.HE↗

arXiv2026

SN~2018erx: A fast-evolving, dust-reddened Type Icn supernova with broad C II emission lines

We present the discovery and characterization of SN~2018erx (ZTF18abkmbpy), a fast-evolving, unusually red, interacting stripped-envelope supernova. Spectroscopically, SN~2018erx shows broad \ion{C}{2} emission with characteristic widths of $\sim\!3800$~km~s$^{-1}$, consistent with interaction with carbon-rich circumstellar material and a Type~Icn core-collapse SN classification. Photometrically, it evolves rapidly, rising from half-maximum to peak in 2.1~d and declining back in 3.1~d. Semi-analytical CSM-interaction modeling favors a compact, shell-like CSM with $M_{\rm CSM}\approx0.3\,M_\odot$, $R_0\approx0.7$~AU, and a low ejecta mass of $M_{\rm ej}\approx0.11\,M_\odot$. The radioactive yield is also small, with $M_{\rm Ni}\lesssim(3$--$5)\times10^{-3}\,M_\odot$, placing SN~2018erx at the low end of the H-poor distribution. At +29~d after peak, we detect a near-infrared excess consistent with pre-existing local circumstellar dust, with $M_{\rm d}\sim10^{-6}$--$10^{-5}\,M_\odot$. Together, the rapid evolution, strong local reddening, carbon-rich emission, and dust point to a multi-component circumstellar environment: a dense inner interaction region from enhanced pre-SN mass loss and an outer dusty layer from 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, with fallback-modified Wolf--Rayet collapse or merger-driven mass loss remaining possible alternatives. SN~2018erx provides rare insight into the mass-loss history of stripped-envelope SNe and suggests that dust-enshrouded explosions of this kind may be underrepresented in optical surveys.

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arXiv2026

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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arXiv2026

Low-Luminosity Type IIP Supernovae from the Zwicky Transient Facility Census of the Local Universe. III: Hunting for electron-capture supernovae using nebular spectroscopy

Electron-capture supernovae (ECSNe) may arise from ONeMg-core collapse in super-asymptotic giant branch (sAGB) stars near the low-mass core-collapse limit ($\approx\!8$--$10$\,\Msun). At early times, models predict that ECSNe resemble low-mass red supergiant iron-core-collapse SNe (FeCCSNe), making the two channels difficult to distinguish. Nebular spectroscopy, however, can reveal differences in ejecta composition. We present a systematic sample of nebular spectra of 19 low-luminosity Type IIP (LLIIP) SNe from the ZTF CLU survey, obtained 115$-$450\,d after explosion. Their low velocities expose narrow lines blended in brighter SNe, which we identify and model to constrain progenitor properties. We find a strong correlation between the FWHM of H\,\textsc{i}\,$λ$6563 and peak luminosity, showing that LLIIP SNe occupy the low-energy end of the core-collapse population, but no correlation with plateau duration, suggesting that envelope and core properties are not tightly linked. Only one SN reaches the extremely low H\,\textsc{i}\,$λ$6563 widths predicted for the weakest $\sim$9\,M$_\odot$ 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 $2.1\pm1.2$. 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 $\lesssim (5$--$8)\times10^{2}\,\mathrm{Gpc^{-3}\,yr^{-1}}$, corresponding to a narrow sAGB progenitor mass window of $ΔM_{\rm sAGB} \lesssim 0.02$--$0.06\,\mathrm{M_\odot}$.

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arXiv2026

A Mass Transferring Brown Dwarf Binary on a 57 Minute Orbit

Mass transfer in stellar binaries has been well studied in most stellar mass ranges, with the notable exception of ultracool stars and substellar brown dwarfs. We report the discovery of ZTF J1239+8347 with the Zwicky Transient Facility (ZTF), a brown dwarf binary currently undergoing stable mass transfer with an orbital period of 57.41 minutes. Optical time-series photometry reveals an extremely high amplitude ($> 2$ magnitude peak-to-trough) variability at short wavelengths indicative of an orbiting hot spot slightly buried inside the atmosphere of the accretor. We use parallax measurements from \textit{Gaia} along with optical and near infrared spectra to infer an accretion temperature of $T_\mathrm{eff} = 8904 \pm 54$ K, an atmospheric temperature of the accretor of $T_\mathrm{atmo} \approx 1500$ K, and a slightly inflated accretor radius of $R_{\rm acc} = 1.20^{+0.15}_{-0.11} \, \RJup$. ZTF J1239+8347 is a direct impact accretor, typically only seen in double degenerate white dwarf binaries, which are approximately a million times denser than the components in ZTF J1239+8347. The existence of an accreting brown dwarf binary suggests that angular momentum loss can be strong enough to make ultracool binaries interact in a Hubble time. The observed faintness ($\sim 20$ mag) and relative proximity ($\approx 300$ pc) of ZTF J1239+8347 suggests that many similar systems are likely to be found by the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST).

astro-ph.SR↗

arXiv2026

The WINTER Observatory: A One-Degree InGaAs Survey Camera to study the Transient Infrared Sky

The Wide-field Infrared Transient Explorer (WINTER) is a near-infrared time-domain survey instrument operating on a dedicated 1-meter robotic telescope at Palomar Observatory. The project takes advantage of recent technology advances in time-domain astronomy, robotic telescopes, large-format sensors, and rapid data reduction and alert software for timely follow up of events. Since June of 2023, WINTER robotically surveys the sky each night to a median depth of J_AB = 18.5 mag, balancing a variety of science programs including searching for kilonovae from gravitational-wave alerts, blind surveys to study galactic and extragalactic transients and variables, and building up reference images of the near-infrared sky. The project also serves as a technology demonstration for new large-format Indium Gallium Arsenide (InGaAs) sensors for wide-field science in the near infrared without cryogenically cooled optics or detectors. WINTER's custom camera combines six InGaAs sensors with a novel tiled fly's-eye optical design to cover a >1 deg^2 field of view with 1 arcsecond pixels in the Y-, J-, and shortened-H-band filters (0.9 - 1.7 micron). This paper presents the design, performance, and early on-sky science of the WINTER observatory.

astro-ph.IM↗

arXiv2026

Multi-color characterization of optically invisible FU Orionis-type outbursts: Demonstration and prospects for the WINTER survey

Episodic mass accretion is the dominant mechanism for mass assembly in the proto-stellar 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 which 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 $\gtrsim 100\times$ fainter than their infrared brightness, demonstrating the capabilities of WINTER to identify heavily obscured young stellar object (YSO) 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, multi-color sensitivity, weekly cadence, and wide area coverage.

astro-ph.SR↗

arXiv2025

Back from the dead: AT2019aalc as a candidate repeating TDE in an AGN

Context. To date, three nuclear transients have been associated with high-energy neutrino events. These transients are generally thought to be powered by tidal disruptions of stars (TDEs) by massive black holes. However, AT2019aalc, hosted in a Seyfert-1 galaxy, was not yet classified due to a lack of multiwavelength observations. Interestingly, the source has re-brightened 4 years after its discovery. Aims. Our aim is to constrain the physical mechanism responsible for the second optical flare, which may also provide clues to the origin of the initial event. Methods. We conducted a multi-wavelength monitoring program (from radio to X-rays) of AT2019aalc during its re-brightening in 2023/2024. Results. The observations revealed multiple X-ray flares during the second optical flaring episode of the transient and a uniquely bright UV counterpart. The second flare, similarly to the first one, is also accompanied by IR dust echo emission. A long-term radio flare is found with an inverted spectrum. Optical spectroscopic observations reveal the presence of Bowen Fluorescence lines and strong high-ionization coronal lines indicating an extreme level of ionization in the system. Conslusions. The results suggest that the transient can be classified as a Bowen Fluorescence Flare (BFF), a relatively new sub-class of flaring active galactic nuclei (AGN). AT2019aalc can be also classified as an extreme coronal line emitter (ECLE). We found that, in addition to AT2019aalc, another BFF AT2021loi is spatially coincident with a high-energy neutrino event. We propose a repeating TDE scenario within an AGN framework to explain the multi-wavelength properties of AT2019aalc and suggest a possible connection among ECLEs, BFFs, and TDEs occurring in AGNs.

astro-ph.HE↗

arXiv2025

ZTF25abjmnps (AT2025ulz) and S250818k: A Candidate Superkilonova from a Sub-threshold Sub-Solar Gravitational Wave Trigger

On August 18, 2025, the LIGO-Virgo-KAGRA collaboration reported gravitational waves from a sub-threshold binary neutron star merger. If astrophysical, this event would have a surprisingly low chirp mass, suggesting that at least one neutron star was below a solar mass. The Zwicky Transient Facility mapped the coarse localization and discovered a transient, ZTF25abjmnps (AT2025ulz), that was spatially and temporally coincident with the gravitational wave trigger. The first week of follow-up suggested properties reminiscent of a GW170817-like kilonova. Subsequent follow-up suggests properties most similar to a young, stripped-envelope, Type IIb supernova. Although we cannot statistically rule out chance coincidence, we undertake due diligence analysis to explore the possible association between ZTF25abjmnps and S250818k. Theoretical models have been proposed wherein sub-solar neutron star(s) may form (and subsequently merge) via accretion disk fragmentation or core fission inside a core-collapse supernova i.e. a ``superkilonova". Here, we qualitatively discuss our multi-wavelength dataset in the context of the superkilonova picture. Future higher significance gravitational wave detections of sub-solar neutron star mergers with extensive electromagnetic follow-up would conclusively resolve this tantalizing multi-messenger association.

astro-ph.HE↗