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Abstract We present detailed radio observations of the tidal disruption event (TDE) ASASSN-19bt/AT 2019ahk, obtained with the Australia Telescope Compact Array, the Atacama Large Millimeter/submillimeter Array, and the MeerKAT radio telescopes, spanning 40–1464 days after the onset of the optical flare. We find that ASASSN-19bt displays unusual radio evolution compared to other TDEs, as the peak brightness of its radio emission increases rapidly until 457 days post-optical discovery and then plateaus. Using a generalized approach to standard equipartition techniques, we estimate the energy and corresponding physical parameters for two possible emission geometries: a nonrelativistic spherical outflow and a relativistic outflow observed from a range of viewing angles. We find that the nonrelativistic solution implies a continuous energy rise in the outflow fromE∼ 10⁴⁶toE∼ 10⁴⁹erg with outflow speedβ≈ 0.05, while the off-axis relativistic jet solution instead suggestsE≈ 10⁵²erg with Lorentz factor Γ ∼ 10 at late times in the maximally off-axis case. We find that neither model provides a holistic explanation for the origin and evolution of the radio emission, emphasizing the need for more complex models. ASASSN-19bt joins the population of TDEs that display unusual radio emission at late times. Conducting long-term radio observations of these TDEs, especially during the later phases, will be crucial for understanding how these types of radio emission in TDEs are produced. 

Abstract We present the first multiepoch broadband radio and millimeter monitoring of an off-nuclear tidal disruption event (TDE) using the Very Large Array, the Atacama Large Millimeter/submillimeter Array, the Allen Telescope Array, the Arcminute Microkelvin Imager Large Array, and the Submillimeter Array. The off-nuclear TDE AT 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 thanF_ν ∼ t⁹at Δt = 88–131 days and then decays as fast asF_ν ∼ t⁻⁶. The emergence of a second radio flare is observed at Δt ≈ 194 days with an initial fast rise ofF_ν ∼ t¹⁸and an optically thin decline ofF_ν ∼ 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 inverse Compton cooling. We find that a single prompt outflow cannot easily explain these observations and that it is likely that either there is only one outflow that was launched at Δt ∼ 80 days or there are two distinct outflows, with the second launched at Δt ∼ 170–190 days. The nature of these outflows, whether sub-, mildly, or ultrarelativistic, 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. 

Abstract We present a comprehensive multi-epoch photometric and spectroscopic study of SN 2024bch, a nearby (19.9 Mpc) Type II supernova (SN) with prominent early high-ionization emission lines. Optical spectra from 2.8 days after the estimated explosion reveal narrow lines of H i, He ii, C iv, and N ivthat disappear by day 6. High-cadence photometry from the ground and Transiting Exoplanet Survey Satellite show that the SN brightened quickly and reached a peakM_V ~ −17.8 mag within a week of explosion, and late-time photometry suggests a⁵⁶Ni mass of 0.050M_⊙. High-resolution spectra from days 7.9 and 43 trace the unshocked circumstellar medium (CSM) and indicate a wind velocity of 30–40 km s⁻¹, a value consistent with a red supergiant (RSG) progenitor. Comparisons between models and the early spectra suggest a pre-SN mass-loss rate of $\dot{M}~10^{-3}–10^{-2}{M}_{\odot }{\mathrm{yr}}^{-1}$, which is too high to be explained by quiescent mass loss from RSGs, but is consistent with some recent measurements of similar SNe. Persistent blueshifted H iand [O i] emission lines seen in the optical and near-IR spectra could be produced by asymmetries in the SN ejecta, while the multicomponent Hαmay indicate continued interaction with an asymmetric CSM well into the nebular phase. SN 2024bch provides another clue to the complex environments and mass-loss histories around massive stars. 

ABSTRACT We examine the properties of ∼50 000 rotational variables from the ASAS-SN survey using distances, stellar properties, and probes of binarity from Gaia DR3 and the SDSS APOGEE survey. They have higher amplitudes and span a broader period range than previously studied Kepler rotators. We find they divide into three groups of main sequence stars (MS1, MS2s, MS2b) and four of giants (G1/3, G2, G4s, and G4b). MS1 stars are slowly rotating (10–30 d), likely single stars with a limited range of temperatures. MS2s stars are more rapidly rotating (days) single stars spanning the lower main sequence up to the Kraft break. There is a clear period gap (or minimum) between MS1 and MS2s, similar to that seen for lower temperatures in the Kepler samples. MS2b stars are tidally locked binaries with periods of days. G1/3 stars are heavily spotted, tidally locked RS CVn stars with periods of 10s of days. G2 stars are less luminous, heavily spotted, tidally locked sub-subgiants with periods of ∼10 d. G4s stars have intermediate luminosities to G1/3 and G2, slow rotation periods (approaching 100 d), and are almost certainly all merger remnants. G4b stars have similar rotation periods and luminosities to G4s, but consist of sub-synchronously rotating binaries. We see no difference in indicators for the presence of very wide binary companions between any of these groups and control samples of photometric twin stars built for each group. 

Abstract Kilonovae, the ultraviolet/optical/infrared counterparts to binary neutron star mergers, are an exceptionally rare class of transients. Optical follow-up campaigns are plagued by contaminating transients, which may mimic kilonovae but do not receive sufficient observations to measure the full photometric evolution. In this work, we present an analysis of the multiwavelength dataset of supernova (SN) 2025ulz, a proposed kilonova candidate following the low-significance detection of gravitational waves originating from the potential binary neutron star merger S250818k. Despite an early rapid decline in brightness, our multiwavelength observations of SN 2025ulz reveal that it is a type IIb SN. As part of this analysis, we demonstrate the capabilities of a novel quantitative scoring algorithm to determine the likelihood that a transient candidate is a kilonova, based primarily on its three-dimensional location and light-curve evolution. We also apply our scoring algorithm to other transient candidates in the localization volume of S250818k and find that, at all times after the discovery of SN 2025ulz, there are ≥4 candidates with a score comparable to SN 2025ulz, indicating that the kilonova search may have benefited from the additional follow-up of other candidates. During future kilonova searches, this type of scoring algorithm will be useful to rule out contaminating transients in real time, optimizing the use of valuable telescope resources. 

Abstract We present panchromatic optical + near-infrared (NIR) + mid-infrared (MIR) observations of the intermediate-luminosity Type Iax supernova (SN Iax) 2024pxl and the extremely low-luminosity SN Iax 2024vjm. JWST observations provide unprecedented MIR spectroscopy of SN Iax, spanning from +11 to +42 day past maximum light. We detect forbidden emission lines in the MIR at these early times while the optical and NIR are dominated by permitted lines with an absorption component. Panchromatic spectra at early times can thus simultaneously show nebular and photospheric lines, probing both inner and outer layers of the ejecta. We identify spectral lines not seen before in SN Iax, including [Mgii] 4.76μm, [Mgii] 9.71μm, [Neii] 12.81μm, and isolated Oi2.76μm that traces unburned material. Forbidden emission lines of all species are centrally peaked with similar kinematic distributions, indicating that the ejecta are well mixed in both SN 2024pxl and SN 2024vjm, a hallmark of pure deflagration explosion models. Radiative transfer modeling of SN 2024pxl shows good agreement with a weak deflagration of a near-Chandrasekhar-mass white dwarf, but additional IR flux is needed to match the observations, potentially attributable to a surviving remnant. Similarly, we find SN 2024vjm is also best explained by a weak deflagration model, despite the large difference in luminosity between the two supernovae. Future modeling should push to even weaker explosions and include the contribution of a bound remnant. Our observations demonstrate the diagnostic power of panchromatic spectroscopy for unveiling explosion physics in thermonuclear supernovae. 

Abstract GRB 221009A ( z = 0.151) is one of the closest known long γ -ray bursts (GRBs). Its extreme brightness across all electromagnetic wavelengths provides an unprecedented opportunity to study a member of this still-mysterious class of transients in exquisite detail. We present multiwavelength observations of this extraordinary event, spanning 15 orders of magnitude in photon energy from radio to γ -rays. We find that the data can be partially explained by a forward shock (FS) from a highly collimated relativistic jet interacting with a low-density, wind-like medium. Under this model, the jet’s beaming-corrected kinetic energy ( E K ∼ 4 × 10 50 erg) is typical for the GRB population. The radio and millimeter data provide strong limiting constraints on the FS model, but require the presence of an additional emission component. From equipartition arguments, we find that the radio emission is likely produced by a small amount of mass (≲6 × 10 −7 M ⊙ ) moving relativistically (Γ ≳ 9) with a large kinetic energy (≳10 49 erg). However, the temporal evolution of this component does not follow prescriptions for synchrotron radiation from a single power-law distribution of electrons (e.g., in a reverse shock or two-component jet), or a thermal-electron population, perhaps suggesting that one of the standard assumptions of afterglow theory is violated. GRB 221009A will likely remain detectable with radio telescopes for years to come, providing a valuable opportunity to track the full lifecycle of a powerful relativistic jet.