Ping Chen

Type Ibn supernovae (SNe) are a class of interacting SNe characterised by narrow helium lines in their spectra. We present an extensive observational dataset of the Type Ibn SN 2025kzr at 51 Mpc, including the discovery of a precursor outburst with a peak brightness of M _r ≈ − 13.6 mag beginning ≈55 days before explosion. Our photometry indicates the SN was discovered within the first day of explosion, and shows fast-rising, ultraviolet-bright emission peaking at M _r = −19.26 ± 0.09 mag and a peak blackbody temperature of T ≈29 000 K, consistent with shock breakout within a region of dense and confined circumstellar material (CSM). Our high-cadence spectroscopic dataset spanning 1.9–58.5 days post-explosion shows flash-ionised emission features during the first ten days. In our SALT spectrum at 3.8 days, we observe a pronounced blueshift of the He II lines by 460 km s ⁻¹ compared to the He I lines at zero velocity, while a Pickering-decrement analysis reveals a CSM that is fully hydrogen free. The timing of the disappearance of the flash features combined with the CSM velocity of 1500 km s ⁻¹ imply a mass-loss event ≈66 days before explosion, in close agreement with the timing of the precursor observed 55 days before explosion and strongly suggestive of a physical link. We derive a CSM mass of 0.03–1.7 M _⊙ and a corresponding high mass-loss rate of ≳10 ⁻¹ M _⊙ yr ⁻¹ . The precursor timescale and energetics suggest an extreme mass-loss event that might be explained by wave-driven mass loss during the late stages of nuclear burning, in particular the oxygen-burning phase. Overall, we favour a single massive Wolf-Rayet progenitor with M _ZAMS ~30–40 M _⊙ to explain SN 2025kzr, although a binary origin cannot be excluded.

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 at t _rest ≈ 50–100 days, with peak radio luminosities ranging from 10 ³⁸ to 10 ⁴⁰ erg s ⁻¹ . Modeling the radio emission as synchrotron radiation indicates a fast ( v = 0.1–0.3 c ) shock in a dense ( n _e ≈ 10 ³ –10 ⁴ cm ⁻³ ) medium. The X-ray emission varies by ≈2 orders of magnitude in luminosity (10 ⁴² –10 ⁴⁴ erg s ⁻¹ ) at t _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 = 10 ⁹ –10 ¹¹ M _⊙ . 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 from t _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.

We present a theoretical framework for the resonance capture and stability of two-planet systems in turbulent disks. By incorporating stochastic forcing (paramterised by ąppa) alongside laminar angular-momentum and eccentricity-damping timescales (τ_ ̊m m , τ_ e ), we derived an analytical criterion for the general j:j-1 mean-motion resonances (MMRs) and validated it through N-body simulations. The outcome is mapped in ąppa-τ_ ̊m m /τ_ e parameter space, revealing two distinct regimes: resonance trapping and turbulence-induced disruption, which occurs either through direct resonance crossing or through temporary capture followed by diffusion-driven escape. Crucially, our analysis identifies turbulence as a universal destabiliser. It amplifies the intrinsic overstability mechanism: In laminar disks, escape requires τ_ ̊m m /τ_ e to drop below a critical limit due to excessive eccentricity excitation. We demonstrate that turbulent diffusion lowers this limit, demanding stronger damping (larger τ_ ̊m m /τ_ e ) for stability. Thus, greater turbulence promotes escape, and sufficiently strong diffusion precludes resonance retention irrespective of eccentricity damping.

We present optical and near-infrared (NIR) observations of the fast-declining Type Ia supernova (SN Ia) 2022an. The photometric and spectroscopic properties identify it as a standard 91bg-like event; however, our data reveal a relatively narrow absorption feature with a full width at half-maximum (FWHM) of 75 Å near 1.037 μ m in the rest frame of the observed spectra that persists from around 30 days to nearly 90 days after maximum light. We attribute this feature to the He i 1.083 μ m line with a blueshifted velocity of 1.3 × 10 ⁴ km s ⁻¹ and a FWHM of 2.1 × 10 ³ km s ⁻¹ , supported by the detection of multiple optical He i transitions at earlier epochs with a higher velocity of around 1.5 × 10 ⁴ km s ⁻¹ . The high velocity of the helium cannot be explained by helium external to the progenitor at the time of explosion, such as stripped surface helium from a companion star. The properties of the helium absorption in the spectra of SN 2022an instead point to unburned material in the outer ejecta, thus providing the most compelling evidence to date for helium-bearing ejecta in a 91bg-like SN Ia. Such helium has been predicted in sub-Chandrasekhar-mass double-detonation explosions involving a surface helium shell. No theoretical calculations of modern helium-shell double detonations have been performed at epochs similar to those observed for SN 2022an to study the effects of helium on their spectra, revealing a gap between observations and theoretical calculations in our understanding of how helium manifests in SNe Ia. Nevertheless, the discovery of persistent helium absorption in SN 2022an demonstrates the diagnostic power of NIR spectroscopy for understanding thermonuclear supernova explosions by probing the abundance and structure of their ejecta.

Context . The Large Array Survey Telescope (LAST) is a wide-field visual-band survey designed to explore the variable and transient sky with high cadence. Its raw data stream is automatically processed in near real time at the observatory site, producing sciencequality images, catalogs, and transient alerts. Transient alerts are then reported to the Transient Name Server (TNS). Aims . The LAST pipeline comprises two major components: (i) processing and calibration of single images followed by the coaddition of 20 × 20 s exposures, producing single-image and coadded-image catalogs; and (ii) the subtraction of coadded images from calibrated reference images followed by transient detection. In this work, we present a detailed description and validation of the second component of the pipeline. Methods . Transient detection is based on the algorithm for proper image subtraction (ZOGY). We combined ZOGY subtraction with the T RANSLIENT statistic for sub-pixel motion discrimination, together with a sequence of deterministic filtering steps, to produce a clean stream of transient candidates without the use of machine learning. Results . Using commissioning data, the pipeline achieves a preliminary 5 σ limiting magnitude of 20.3-20.7 mag, a single-epoch transient detection efficiency of ∼80%, and a purity of ≳90% at a signal-to-noise ratio of ≥7.5 σ .

Context. The origins of astrophysical high-energy neutrino flux remain uncertain. Core-collapse supernovae (CCSNe) with strong circumstellar material (CSM) interactions (i.e., Type IIn, a.k.a. SNe IIn) are compelling candidates for explaining efficient hadronic acceleration and neutrino production. Aims. We investigate the possible association between the SNe IIn SN2025cbj and the IceCube high-energy neutrino IceCube-250421A. We assess whether the observed properties of the SN would enable an appreciable neutrino yield. Methods. We combined rapid optical follow-ups with LAST and archival ZTF photometry with spectroscopy from LT/SPRAT and MMT/BINOSPEC to characterize the SN’s evolution and CSM interaction. We estimated the explosion and peak times from an early light-curve fitting and quantified the chance-coincidence probability with resampling simulations that scramble neutrino right ascensions, while preserving declinations and error contours. Using a simple post-shock-breakout interaction model in a dense wind, we estimated the expected muon-neutrino yield for IceCube’s real-time Bronze stream. Results. The spectra of SN2025cbj obtained after the neutrino epoch exhibit persistent narrow Balmer lines superposed on broad Lorentzian electron-scattering wings, consistent with a sustained dense CSM interaction. For the multimessenger association, resampling the simulations against the TNS catalog gives a chance-coincidence p -value of p ≃ 0.24 for observing k ≥ 1 events (and p ≃ 0.078 against the ZTF-BTS catalog). These values are sensitive to the size of the SN and neutrino samples and do not indicate a statistically significant multimessenger association. A post-breakout interaction scenario predicts an expected N ν _μ ∼ 10 ⁻³ events in the IceCube Bronze alert stream over 96 days per this one candidate. We discuss the implications of these numbers and the possible biases that could affect these results.

We initiate the systematic search for planets in the 2023 data of the Korea Microlensing Telescope Network (KMTNet), focusing on those planets found by the KMTNet AnomalyFinder with low preliminary estimates of the mass ratio, q < 2 × 10 ⁻⁴ . The 2023 season is the first for which the photometry of all events was re-reduced prior to the AnomalyFinder search, potentially increasing its sensitivity to planets. We find three strong low- q planet candidates, KMT-2023-BLG-0164 ( q ∼ 1.3 × 10 ⁻⁴ ), KMT-2023-BLG-1286 ( q ∼ 1.9 × 10 ⁻⁴ ), and KMT-2023-BLG-1746 ( q ∼ 8 × 10 ⁻⁵ ). KMT-2023-BLG-0164 is notable in that the source is projected on a very bright ( I = 16.0) foreground star, which is either the planet’s host or (more likely) a companion to the host. We obtain a spectrum, finding that its mass and distance are M ∼ 1.0 M _⊙ and D ∼ 1.5 kpc, respectively, the latter being the distance of the lens ( D _L ) regardless of whether the spectroscopic target is the host or its companion. We also analyze two other candidates, KMT-2023-BLG-0614 and KMT-2023-BLG-1593, which are unlikely to enter the statistical sample owing to their ambiguous interpretations as possible nonplanetary events.

Context . The formation of planetesimals via the streaming instability (SI) is a crucial step in planet formation, yet its triggering conditions and efficiency are highly sensitive to both disk properties and specific evolutionary processes. Aims . We aim to study the planetesimal formation via the SI, driven by the stellar X-ray photoevaporation during the late stages of disk dispersal, and to quantify its dependence on key disk and stellar parameters. Methods . We used the DustPy code to simulate the dust evolution, including coagulation, fragmentation, and radial drift, in a viscously accreting disk undergoing stellar X-ray photoevaporation. Results . Stellar X-rays drive the disk dispersal, opening a cavity at orbital radii of a few au and inducing the formation of an associated local pressure maximum. This pressure maximum acts as a trap for radially drifting dust, therefore enhancing the dust density to the critical level required to initiate the streaming instability and the subsequent collapse into planetesimals. The fiducial model produces 31.4 M _⊕ of planetesimals with an initial dust to final planetesimal conversion efficiency of 20.4%. This pathway is most efficient in larger disks with higher metallicities, lower viscosities, higher dust fragmentation threshold velocities, and/or around stars with higher X-ray luminosities. Conclusions . This work demonstrates that stellar X-ray photoevaporation is a robust and feasible mechanism for triggering planetesimal formation via the SI during the final clearing phase of protoplanetary disk evolution.

We present extensive ultraviolet to optical photometric and optical to near-infrared (NIR) spectroscopic follow-up observations of the nearby intermediate-luminosity ( M _V = −16.81 ± 0.19 mag) Type Iax supernovae (SNe Iax) 2024pxl in NGC 6384. SN 2024pxl exhibits a faster light curve than the high-luminosity members of this class, and slower than low-luminosity events. The observationally well-constrained rise time of ∼11 days and an estimated synthesized ⁵⁶ Ni mass of 0.03 M _⊙ , based on analytical modeling of the integrated spectral energy distribution light curve, are consistent with models of the weak deflagration of a carbon-oxygen white dwarf. Our optical spectral sequence of SN 2024pxl shows weak Si ii lines and spectral evolution similar to other high-luminosity SNe Iax, but also a prominent early-time C ii line, like lower-luminosity SNe Iax. The late-time optical spectrum of SN 2024pxl closely matches that of SN 2014dt, and its NIR spectral evolution aligns with that of other well-studied, high-luminosity SNe Iax. The spectral-line expansion velocities of SN 2024pxl are at the lower end of the SNe Iax velocity distribution, and the velocity distribution of iron-group elements compared to intermediate-mass elements suggests that the ejecta are mixed on large scales, as expected in pure deflagration models. SN 2024pxl exhibits characteristics intermediate between those of high-luminosity and low-luminosity SNe Iax, further establishing a link across this diverse class.