Keiichi Maeda

The final life stages of the massive star progenitors of stripped-envelope supernovae (SESNe) remain an open question, especially when it comes to the timing and magnitude of the progenitor stripping. Observing SESNe across the electromagnetic spectrum allows for the most direct constraints on mass loss in the final stages of progenitor evolution. In this work, we present radio (GMRT+VLA) and X-ray (Swift+Chandra) observations of SN 2019yvr obtained from 18 to 1784 days postexplosion. SN 2019yvr was a Type Ib supernova (SN Ib, with strong helium but little or no hydrogen ) that transitioned into a Type IIn supernova (SN IIn, with shock-driven hydrogen features from interaction with circumstellar material, CSM) at ∼100 days postexplosion. The radio evolution is best fit by a synchrotron self-absorbed model with a ρ ∝ r ^{−1.54±0.31} CSM density profile, suggesting a decreasing mass-loss rate from the progenitor in the years leading up to the explosion. The radio-derived shock speed is high, more than 30,000 km s ⁻¹ at early times, suggesting a compact progenitor star. The combined radio and X-ray data probe CSM that extends from 1.7 × 10 ¹⁶ cm up to ∼20 × 10 ¹⁶ cm and was created by mass loss from ∼(1−3) × 10 ⁻⁵ M _⊙ yr ⁻¹ (assuming a CSM speed of 100 km s ⁻¹ ). The combined dataset rules out any dramatic jump in CSM density (which was seen in the optical analog SN 2014C) associated with the emergence of optical hydrogen emission lines. We place SN 2019yvr in context with similar transitional SNe and discuss implications for the progenitor.

Tidal disruption events (TDEs) are believed to launch outflows that play a crucial role in producing optical emission lines. In this study, we investigate emission properties expected within the wind-driven outflow framework, in which an outflow is continuously injected from the central engine. We perform radiative transfer calculations to compute synthetic line properties and apply the model to the optical TDE ASASSN-14ae. We find that a two-component structure with a high density contrast, consisting of an optically thick inner layer and an optically thin outer layer, is required to simultaneously reproduce the observed photospheric and H α properties. The optically thin component exhibits a power-law temporal evolution in the mass-outflow rate and kinetic power, with the total ejected mass of ∼0.25 M _⊙ , indicating that it might originate in a super-Eddington accretion-disk-driven outflow. The optically thick component is responsible for the photospheric emission, and we argue that this component is more plausibly interpreted as a quasi-hydrostatic envelope rather than an outflow. Interestingly, the kinetic power of the optically thin component and the bolometric luminosity originating from the optically thick component are comparable, and they share the same temporal evolution. This finding indicates that these two components are energetically linked through an equipartition process—pointing to a scenario in which the accretion energy is first converted to the kinetic energy of the outflow, and then this energy is dissipated to the envelope through the outflow–envelope interaction before it emerges from the surface of the envelope.

We present multiwavelength photometric and optical spectroscopic observations of the long-lived interacting supernova SN 2019vxm, spanning more than 2 yr after the explosion. SN 2019vxm is a slowly rising (rise time ∼ 43 days in the R -band), slowly declining supernova reaching an R -band peak absolute magnitude of ≈−20.3 mag. The SN light curve postmaximum shows a shallow decline, followed by a secondary, steeper decline in the optical (∼0.01 mag day ⁻¹ ), with late-time IR brightening. The total radiated luminosity is 5 × 10 ⁵⁰ erg, placing it among the energetic class of its type. We estimated a CSM mass of 3–8 M _⊙ through light-curve modeling (independent of the CSM density profile) and by comparison with theoretical models. We estimate a minimum ejecta mass of ∼3.88 M _⊙ from the broad H α component, consistent with the ejecta mass obtained from the light-curve models. The solely interaction-dominated initial epochs are later accompanied by photon-scattering signatures, leading to asymmetric line profiles with symmetric wings. The late phase, characterized by enhanced brightness at longer wavelengths and a stronger asymmetric line profile with the red side flux strongly suppressed, indicates the influence of preexisting or newly formed dust with temperatures ∼1600 K at ∼4 × 10 ¹⁶ cm. Even in the late phases, no nebular lines are present in the spectra, indicating dense or obscured ejecta.

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 panchromatic observations of the Type Ia supernova (SN Ia) 2023qov, ranging from ∼2 weeks before to ∼1 yr after maximum light. JWST near- and mid-infrared spectra at +276 and +363 days show ∼400 K dust emission that cools by ∼75 K between epochs, the first unambiguous spectroscopic detection of dust emission in a normal SN Ia. We find that the emission is well described by models of carbonaceous dust placed within ∼1 lt-yr of the SN, with a dust mass of ∼10 ⁻⁴ M _⊙ . We do not see evidence of active dust creation, suggesting an infrared light echo by preexisting circumstellar dust as the likely source of the emission. The JWST nebular line profiles suggest asymmetric, stratified ejecta, similar to other normal SNe Ia, though a slight double-horn structure in the argon lines indicates a toroidal enhancement. SN 2023qov exhibits a slightly red, fast-declining early light curve (Δ m ₁₅ ( B ) = 1.47 ± 0.05 mag), from which we determine a ⁵⁶ Ni mass of M ₅₆ = 0.21 ± 0.04 M _⊙ , and a distance of d = 36.0 ± 1.8 Mpc to the SN and its host, NGC 7029. The presence of circumstellar dust around a normal SN Ia has implications both for the progenitor system, suggesting a less than pristine environment, and for cosmology, as a possible source of reddening and extinction that can affect distance inferences.

We present near-infrared (NIR) and optical observations of the highly reddened Type IIP supernova (SN) 2023gfo in the nearby galaxy NGC 4995 ( d = 26.4 ± 3.2 Mpc), which reached a high peak luminosity of M _V = −18.6 mag. The SN was initially detected as a faint red event, with B − V = 0.8 mag at the beginning of the plateau phase. By comparison with the template, we estimate a total extinction of A _V = 2.1 mag. After correcting for this extinction, we derive a peak quasi-bolometric luminosity of (5.9 ± 1.5) × 10 ⁴² erg s ⁻¹ , placing this event among the most luminous SNe IIP, while its plateau duration remains within the normal range. The early-phase optical spectrum exhibits a P-Cygni profile of H α , with a broad absorption of V = 13,800 km s ⁻¹ , which is among the highest observed for SNe IIP at comparable epochs. The high luminosity and the normal plateau duration suggest that this event represents an outlier. Applying an analytical model, we infer an unusually large progenitor radius. This may indicate that the progenitor experienced an extreme energy injection from the core to the envelope shortly before explosion, resulting in a substantially inflated radius. While ejecta–circumstellar matter (CSM) interaction could in principle account for the high luminosity, we find no observational evidence supporting strong interaction.

Quasiperiodic eruptions (QPEs) and recurrent nuclear transients (RNTs) exhibit recurrent high-amplitude flares from galactic nuclei, yet their characteristic timescales remain poorly understood. In this work, we compile a sample of these systems and investigate empirical scaling relations between flare timescales and black hole masses. We find that the recurrence timescale exhibits a positive but highly scattered dependence on black hole mass in the combined QPE and RNT sample, approximately following t rec ∝ M BH 1.1 9 − 0.47 + 0.52 with an intrinsic scatter of 0.95 dex. Remarkably, we uncover a tight, nearly linear relation between recurrence time and flare timescale for QPEs and RNTs, described by t rec ∝ t rise 1.00 ± 0.07 with an intrinsic scatter of 0.29 dex. This relation extends across timescales from hours for QPEs to months and years for nuclear transients. We further find that QPEs and RNTs approximately follow a common empirical relation between recurrence time and flare rise time, although the physical origin of this relation remains uncertain. Our findings reveal a common phenomenological timescale link across RNTs, providing a practical framework for characterizing their temporal behavior.

Understanding dust attenuation toward extragalactic transients is critical for recovering their intrinsic properties and probing the local environments of distant galaxies. A popular diagnostic is the Na i D absorption equivalent width, widely applied to extragalactic transients. In this paper, we present early-time optical and near-infrared observations of the Type Ib supernova (SN Ib) SN 2024vjc, followed for ∼130 days postexplosion. SN 2024vjc exhibits only weak Na I D absorption, indicating only a modest host attenuation with E ( B − V ) _host ∼ 0.18 mag; if this argument were applied, SN 2024vjc would be a peculiar, faint, and red SN Ib while showing the light-curve shape and spectral evolution broadly consistent with those of canonical Type Ib supernovae. We show that this is not the case; SN-based diagnostics (intrinsic color templates, color-curve evolution, and spectral dereddening) together with the Balmer decrement indicate substantial attenuation, E ( B − V ) ∼ 0.45−0.8 mag. The weak Na i D absorption may result from photoionization of neutral sodium by the intense radiation field of a young H ii region at the explosion site; this scenario is directly supported by the detection of narrow H α , [N ii ], and H β emission lines and a blue continuum excess in late-time spectroscopy. SN 2024vjc represents a clear counterexample to the common assumption that weak or absent Na I D absorption implies negligible host-galaxy attenuation, and highlights the importance of employing multiple, independent attenuation diagnostics.

The explodability of massive stars, namely whether they undergo core-collapse supernovae (CCSNe) or form black holes (BHs), strongly influences galactic chemical evolution (GCE). Details of the explodability are still controversial, but realistic predictions including metallicity dependence are becoming available through stellar-evolution and explosion calculations. In the present work, we implement recently proposed metallicity-dependent explodability prescriptions into a GCE framework. We show that the physics-motivated explodability prescriptions reproduce the key observed abundance trends. Further, within uncertainties of the explodability models, the GCE model provides important constraints on the region of the BH formation in the mass–metallicity space. Guided by these findings, we further construct a simplified form of the metallicity-dependent explodability designed to alleviate the red supergiant (RSG) problem and explore its compatibility with GCE constraints. We find that such a solution exists, if (1) the net outflows from the system are negligible/absent and (2) the transition of the explodability takes place at subsolar metallicity. These results demonstrate that GCE can provide meaningful constraints on massive-star explodability and that explodability prescriptions capable of addressing the RSG problem can be constructed without violating chemical-evolution observables. We also show that a metallicity-dependent initial mass function can improve agreement with observations; this effect becomes important once coupled with the metallicity-dependent explodability.