Yi Yang

We present a photometric and spectroscopic study of the superluminous Type Ia supernova SN 2022erq. Its early spectra, dominated by iron-group elements with weak intermediate-mass features, might indicate highly efficient nuclear burning, broadly similar to that inferred for some overluminous Type Ia supernovae. The rapid emergence and persistence of narrow Balmer emission lines superposed on this iron-rich spectrum provide clear evidence of long-lived interaction with a hydrogen-rich circumstellar medium (CSM), establishing SN 2022erq as a member of the rare Ia–CSM class. SN 2022erq reached a peak bolometric luminosity of ∼8 × 10 ⁴³ erg s ⁻¹ and exhibited an exceptionally slow postpeak decline, indicating that its light curve is dominated by long duration ejecta–CSM interaction. By combining H α diagnostics with bolometric light-curve modeling, we reconstruct the preexplosion mass-loss history of the progenitor. The mass-loss rate escalated by 1 order of magnitude over the final decades, rising from ∼0.04 to ∼0.6 M _⊙ yr ⁻¹ . This surge produced a massive, extended CSM shell of ∼3 M _⊙ out to ∼3.5 × 10 ¹⁶ cm. The young stellar environment (∼100 Myr) together with this substantial, extensive CSM points to a progenitor system consisting of a white dwarf and an intermediate-mass companion that underwent increasing mass loss prior to explosion.

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 new James Webb Space Telescope (JWST) mid-infrared (MIR) spectra and ground-based optical spectra of the lingering source at the position of supernova (SN) 2010jl, which was a relatively nearby superluminous Type IIn supernova (SLSN IIn) having strong interaction with circumstellar material (CSM). Early-time data showed evidence of dust, interpreted as either preexisting CSM dust, or as newly formed dust in the SN ejecta and postshock region. At 13 yr post explosion, JWST reveals a strong MIR excess from warm dust, with broad features at 10–15 μ m. Our analysis reveals a minimum dust mass of >0.11 M _⊙ , and a more likely value of 0.2 M _⊙ or more because the dust is optically thick. This is among the largest masses of SN-produced dust yet measured without far-IR/submillimeter data, and greatly exceeds SN 2010jl’s dust mass inferred around 2–3 yr postexplosion. Ground-based optical spectra confirm the presence of a young massive cluster at the SN position and confirm that blueshifted line profiles persisting until the latest epochs arise from dust formed in the postshock region. The warmest dust emitting in the MIR is likely to be the same post-shock dust causing the blueshift. The JWST spectrum also reveals silicate absorption, which may arise from cool SN ejecta dust along the line of sight to the receding shock. The large mass of postshock dust in SN 2010jl suggests that strong CSM interaction promotes efficient dust production, where the new postshock dust will survive. If strongly interacting SNe are common in the early Universe, this may contribute significantly to dust seen in infant galaxies.

We present a comprehensive multiwavelength analysis of the long-duration gamma-ray burst (GRB) 250424A. Our dataset spans from the prompt gamma-ray emission to late-time optical monitoring, including spectra obtained with the Keck 10 m telescope. We find that the afterglow light curves display a prominent, simultaneous shallow decay phase in both X-ray and optical bands, followed by an achromatic transition to a standard decay regime. The broadband spectral energy distributions are well modeled by a single power-law function, indicating a common synchrotron origin for the emission across frequencies. We interpret the afterglow evolution within the framework of a relativistic forward shock refreshed by continuous energy injection. This scenario successfully reproduces the observed temporal and spectral behavior, yielding an isotropic equivalent kinetic energy of E_K,iso ≈ 5.5 × 10⁵² erg and an injection index of q ≈ 0.34 in a constant-density circumburst environment. The shallow decay phase is consistent with sustained energy injection lasting ∼9 ks. Despite the relatively low redshift, late-time optical observations reveal no distinct supernova component; however, our derived upper limits do not strictly rule out the presence of a typical GRB-associated supernova.

We present optical + near-infrared + mid-infrared (MIR) observations of the normal Type Ia supernovae (SNe Ia) 2022aaiq and 2024gy in the nebular phase, continuously spanning 0.35–28 μ m. Medium-resolution JWST spectroscopy reveals novel narrow ( v _FWHM < 1500 km s ⁻¹ ) [Ni ii ] 1.94 and 6.64 μ m cores in both events. The MIR [Ni ii ] 6.64 μ m line exhibits a distinct narrow core atop a broader base, indicating a central enhancement of stable Ni. This structure points to high central densities consistent with a near-Chandrasekhar-mass ( M _Ch ) progenitor or a high-metallicity sub- M _Ch progenitor. From detailed line-profile inversions of SN 2024gy, we derive emissivity profiles for stable iron-group elements, radioactive material, and intermediate-mass elements, revealing spatially distinct ejecta zones. The [Ni iii ] 7.35 μ m line shows a shallow-to-steep slope transition—a “broken-slope” morphology—that matches predictions for delayed detonation explosions with separated deflagration and detonation ashes. We also reanalyze and compare to archival JWST spectra of SN 2021aefx and the subluminous SN 2022xkq. From the stable Ni luminosities, we infer that SN 2024gy produced ∼5–10 times more stable Ni mass than SN 2022xkq, favoring a near- M _Ch scenario for SN 2024gy and a sub- M _Ch scenario for SN 2022xkq. These results demonstrate that resolved line profiles, now accessible with JWST, provide powerful diagnostics of explosion geometry, central density, and progenitor mass in SNe Ia.

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.

We present a physical characterization of Tsinghua University-Ma Huateng Telescope for Survey (TMTS) J00063798+3104160 (J0006), a rapidly rotating, ultramassive white dwarf (WD) identified in high-cadence light curves from the TMTS. A coherent 23 minute periodicity is detected in TMTS, Transiting Exoplanet Survey Satellite, and Zwicky Transient Facility photometry. A time series of low-resolution spectra with the Keck-I 10 m telescope reveals broad, shallow hydrogen absorption features indicative of an extreme magnetic field and shows no evidence for radial-velocity variations. Atmospheric modeling yields a magnetic field strength of ∼250 MG, while Gaia astrometry and photometry imply a mass of 1.06 ± 0.01 M _⊙ . A significant infrared excess is detected in the Wide-field Infrared Survey Explorer W1 band and is well fitted by a 550 K blackbody, likely arising from residual material of a merger. We interpret the 23 minute photometric modulation as the rotation period of an isolated, massive WD formed likely through the merger of a double WD binary. With one of the shortest rotation periods known among candidate merger remnants and with constraints from a deep Einstein Probe X-ray nondetection, J0006 provides a rare and important observational window into the poorly explored intermediate stages of postmerger evolution.

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 days. AT 2024wpp is the most luminous LFBOT discovered to date, with L _pk ≈ (2–4) × 10 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 days, 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 a peak of T > 30,000 K and R _BB / t ≈ 0.2 c –0.3 c . We find evidence for cooling until ∼10 days; thereafter, T ≳ 20,000 K is maintained. We interpret the featureless spectra as a consequence of continuous energy injection from a central source of high-energy emission that maintains high ejecta ionization. After 35 days, faint (equivalent width (EW) ≲ 10 Å) H and He spectral features with kinematically separate velocity components centered at 0 and −6400 km s ⁻¹ emerge, implying spherical symmetry deviations. A near-infrared excess of emission above the optical blackbody emerges between 20 and 30 days, with a power-law spectrum F _{ν ,NIR} ∝ ν ^−0.3 at 30 days. 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.