Kishore C. Patra

We present multiwavelength observations and analysis of SN 2024iss, a Type IIb supernova (SN IIb) located at ∼14 Mpc. The first Zwicky Transient Facility detection of SN 2024iss is ∼40 minutes after first light (one of the earliest detections of a SN IIb to date) and a Hubble Space Telescope (HST) UV spectrum was obtained at 7 days (the earliest HST UV SN IIb spectrum to date). We estimate an ejecta mass range of 1.1–3.3 M _⊙ and a ⁵⁶ Ni mass of 0.11 ± 0.01 M _⊙ from bolometric light-curve modeling and He-star model comparisons. We fit shock-cooling emission models to estimate a progenitor radius of 100–320 R _⊙ and an envelope mass of 0.07–0.46 M _⊙ . We compare optical/UV spectra to binary progenitor models, which indicate a stripped H-rich envelope mass of 0.19–0.28 M _⊙ . We use early-time X-ray detections to calculate circumstellar material (CSM) densities that are consistent with a progenitor mass-loss rate of 5 × 10 ⁻⁴ M _⊙ yr ⁻¹ ( v _w = 100 km s ⁻¹ ), corresponding to 2–5 yr preexplosion. In the UV, we observe strong Mg ii emission extending to 15,000 km s ⁻¹ as well as weak P Cygni profiles of iron-group elements (e.g., Fe, Ti, Al, Ni) present in outer SN ejecta. The overall spectroscopic evolution of SN 2024iss is comparable to that of SNe IIb, but its increased brightness at peak is influenced by SN ejecta–CSM interaction. Nebular spectroscopy of SN 2024iss at ∼260–412 days reveals multipeaked forbidden-line profiles of O i and Mg i ] indicative of inner ejecta asymmetry and/or clumping. We demonstrate the utility of a rich, multiwavelength data set for constraining the progenitor systems and explosion dynamics of SNe IIb.

We present optical and near-infrared (NIR) observations of the Type Ib supernova (SN) 2024rbc. Emission from the first CO overtone, resting on a dust continuum at 2.3−2.4 μ m, was observed at 62 days postexplosion. The CO band heads are not resolved, and the emission appears broad, lacking sharp spectral features. This is the first observation of CO in the ejecta of a Type Ib SN reported in literature. The spectra of SN 2024rbc exhibit strong He I lines and numerous neutral and ionized metal lines. Comparing the spectral evolution of SN 2024rbc to other Type Ib, Ic, and IIb SNe indicates it is a Type Ib SN. We compare the velocities of key optical lines to examine the evolution of the ejecta. Additionally, fitting SN light-curve models of helium star progenitors computed with the STELLA code to photometric observations indicates a ⁵⁶ Ni mass of 0.07 M _⊙ and an ejecta mass of 1.7 M _⊙ . Fitting an LTE model to the CO overtone implies a CO mass of 5.2 × 10 ⁻⁴ M _⊙ , a CO temperature of 4040 K, and a CO velocity width of 5905 km s ⁻¹ . We also fitted a modified blackbody model to the dust continuum, deriving a dust temperature of 910 K and a dust mass of 1.3 × 10 ⁻³ M _⊙ . The CO provides direct evidence for the onset of dust formation, and the observed dust continuum likely originates from newly formed dust in the ejecta. However, robust dust mass estimates require mid-infrared (MIR) observations.

We present new transit-timing measurements for the white dwarf-cold Jupiter system WD 1856+534, extending the baseline of observations from 311 epochs to 1498 epochs. The planet is unlikely to have survived the host star’s red-giant phase at its present location and is likely too small for common envelope evolution to take place. As such, a plausible explanation for the short semimajor axis is that the exoplanet started out on a much larger orbit and then spiraled inward through high-eccentricity tidal migration (HETM). A past study found tentative evidence for orbital growth, which could have been interpreted as a residual effect of HETM, but we find the data are consistent with a constant-period model after adding 18 new transit measurements. We use the estimated period derivative P ̇ = 0.04 ± 0.43 ms yr ⁻¹ to place a lower limit on the planetary tidal quality factor of Q p ′ ≳ 3.1 × 1 0 6 , if the planet has not already achieved spin–orbit synchronization. We also test for the presence of companion planets in the system, which could have excited WD 1856 b onto an eccentric orbit via the Kozai–Lidov process, and ultimately rule out the presence of an additional planet with mass greater than 4.0 M _J and period shorter than 1500 days. We find no evidence for nonzero eccentricity, with an upper limit of e ≲ 10 ⁻² . If the planet reached its current orbit through HETM, the low present-day eccentricity indicates that the migration process has now ceased, and any further orbital evolution, if any, will likely be governed by weak planetary tides.

Supernova (SN) 2025coe at a distance of ∼25 Mpc is the second-closest calcium-strong transient. It was discovered at a large projected offset of ∼34 kpc from its potential host galaxy NGC 3277. Multiband photometry of SN 2025coe indicates the presence of two peaks at day ∼2 and day ∼11 after explosion. Modeling the bolometric light curve, we find that the first peak can be reproduced either by shock cooling of a compact envelope ( R _env ≈6–40 R _⊙ ; M _env ≈0.1–0.2 M _⊙ ) or by interaction with close-in circumstellar material (CSM; R _CSM ≲ 6 × 10 ¹⁴ cm), or a combination of both. The second peak is dominated by radioactive decay of ⁵⁶ Ni ( M _ej ≈ 0.4–0.5 M _⊙ ; M 56 Ni ≈ 1.4 × 1 0 − 2 M _⊙ ). SN 2025coe rapidly evolves from the photospheric phase dominated by He I P Cygni profiles to nebular phase spectra dominated by strong [Ca ii ] λλ 7291, 7323 and weak [O i ] λλ 6300, 6364 emission lines. Simultaneous line profile modeling of [Ca ii ] and [O i ] at nebular phases shows that an asymmetric core-collapse explosion of a low-mass (≲3.3 M _⊙ ) He-core progenitor can explain the observed line profiles. Alternatively, lack of local star formation at the site of the SN explosion combined with a low ejecta mass is also consistent with a thermonuclear explosion due to a low-mass hybrid He-C/O white dwarf +C/O white dwarf merger.

We present complete spectropolarimetric coverage of the Type II supernova (SN) 2023ixf, ranging from 1 to 120 days after explosion. Polarimetry was obtained with the Kast double spectrograph on the Shane 3 m telescope at Lick Observatory. As the ejecta interact with circumstellar material (CSM) during the first week, the intrinsic polarization of SN 2023ixf is initially high at ≲1%, dropping steeply within days down to ∼0.4% when the ejecta sweep up the optically thick CSM. The continuum polarization stays low at ∼0.2% thereafter, until it rises again to ∼0.6% as the ejecta transition to the nebular phase. We model this evolution using a combination of archival and newly computed two-dimensional polarized radiative transfer models. In this context, we interpret the early-time polarization as arising from an aspherical CSM with a pole-to-equator density contrast of ≳3. We propose that the surge in polarization at late times originates from an asymmetric distribution of ⁵⁶ Ni deep in the ejecta. The distinct sources of asymmetries at early and late times are consistent with the temporal evolution of the observed polarization and the polarization angle in SN 2023ixf.

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 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.

The death of massive stars is triggered by an infall-induced bounce shock that disrupts the star. How such a shock is launched and propagates through the star is a decade-long puzzle. Some models assume that the shock can be reenergized by absorbing neutrinos, leading to highly aspherical explosions. Other models involve jet-powered shocks that lead to bipolar explosions reflected in the geometry of the shock-breakout emission. We report measurement of the geometry of the shock breakout through unprecedentedly early spectropolarimetry of the nearby type II supernova 2024ggi starting ~1.2 days after the explosion. The measurement indicates a well-defined symmetry axis of the shock breakout, which is also shared by the hydrogen-rich envelope that emerged after the circumstellar matter was engulfed by the ejecta, revealing a persisting and prominent symmetry axis throughout the explosion. These findings suggest that the physical mechanism driving the explosion of massive stars manifests a well-defined axial symmetry and acts on large scales.

We present multiwavelength observations of the Type II supernova (SN II) 2023ixf during its first 2 yr of evolution. We combine ground-based optical/near-infrared spectroscopy with Hubble Space Telescope far- and near-ultraviolet spectroscopy and James Webb Space Telescope near- and mid-infrared photometry and spectroscopy to create spectral energy distributions of SN 2023ixf at +374 and +620 days postexplosion, covering a wavelength range of ∼0.1–30 μ m. The multiband light curve of SN 2023ixf follows a standard radioactive decay decline rate after the plateau until ∼500 days, at which point shock-powered emission from ongoing interaction between the SN ejecta and circumstellar material (CSM) begins to dominate. This evolution is temporally consistent with 0.3–10 keV X-ray detections of SN 2023ixf and broad “boxy” spectral line emission, which we interpret to signal reprocessing of shock luminosity in a cold dense shell located between forward and reverse shocks. Using the expected absorbed radioactive decay power and the detected X-ray luminosity, we quantify the total shock-powered emission at the +374 and +620 day epochs and find that it can be explained by nearly complete thermalization of the reverse shock luminosity as SN 2023ixf interacts with a continuous, “wind-like” CSM with a progenitor mass-loss rate of M ̇ ≈ 1 0 − 4 M _⊙ yr ⁻¹ ( v _w = 20 ± 5 km s ⁻¹ ). Additionally, we construct multiepoch spectral models from the non-LTE radiative transfer code CMFGEN that contain radioactive decay and shock powers as well as dust absorption, scattering, and emission. We find that models with shock powers of L _sh = (0.5–1) × 10 ⁴⁰ erg s ⁻¹ and ∼(0.5–1) × 10 ⁻³ M _⊙ of silicate dust in the cold dense shell and/or inner SN ejecta can effectively reproduce the global properties of the late-time (>300 days) UV-to-IR spectra of SN 2023ixf.