More Like this

1. Expanding the parameter space of 2002es-like type Ia supernovae: On the underluminous ASASSN-20jq/SN 2020qxp

   https://doi.org/10.1051/0004-6361/202553687  

   Bose, S; Stritzinger, M D; Ashall, C; Baron, E; Hoeflich, P; Galbany, L; Hoogendam, W B; Jensen, E_A M; Kochanek, C S; Post, R S; et al (July 2025, Astronomy & Astrophysics)

   We present optical photometric and spectroscopic observations of the peculiar Type Ia supernovae (SNe Ia) ASASSN-20jq/SN 2020qxp. It is a low-luminosity object, with a peak absolute magnitude ofM_B = −17.1 ± 0.5 mag, while its post-peak light-curve decline rate of Δm₁₅(B) = 1.35 ± 0.09 mag and color-stretch parameter ofs_BV ⪆ 0.82 is similar to that of normal luminosity SNe Ia. That makes it a prevalent outlier in both the SN Ia luminosity-width and the luminosity-color-stretch relations. The analysis of the early light curves indicates a possible “bump” during the first ≈1.4 days of explosion. ASASSN-20jq synthesized a low radioactive⁵⁶Ni mass of 0.09 ± 0.01 M_⊙. The near-maximum light spectra of the supernova show strong Si IIabsorption lines, indicating a cooler photosphere than normal SNe Ia; however, it lacks Ti IIabsorption lines. Additionally, it shows unusually strong absorption features of O Iλ7773 and the Ca IInear-infrared triplet. The nebular spectra of ASASSN-20jq show a remarkably strong but narrow forbidden [Ca II]λλ7291, 7324 doublet emission that has not been seen in SNe Ia except for a handful of Type Iax events. There is also a marginal detection of the [O I]λλ6300, 6364 doublet emission in nebular spectra, which is extremely rare. Both the [Ca II] and [O I] lines are redshifted by roughly 2000 km s⁻¹. ASASSN-20jq also exhibits a strong [Fe II]λ7155 emission line with a tilted-top line profile, which is identical to the [Fe II]λ16433 line profile. The asymmetric [Fe II] line profiles, along with the redshifted [Ca II] and emission lines, suggest a high central density white dwarf progenitor that underwent an off-center delayed-detonation explosion mechanism, synthesizing roughly equal amounts of⁵⁶Ni during the deflagration and detonation burning phases. The equal production of⁵⁶Ni in both burning phases distinguishes ASASSN-20jq from normal bright and subluminous SNe Ia. Assuming this scenario, we simultaneously modeled the optical and near-infrared nebular spectra, achieving a good agreement with the observations. The light curve and spectroscopic features of ASASSN-20jq do not align with any single sub-class of SNe Ia. However, the significant deviation from the luminosity versus light-curve shape relations (along with several light-curve and spectroscopic features) exhibits similarities to some 2002es-like objects. Therefore, we have identified ASASSN-20jq as an extreme candidate within the broad and heterogeneous parameter space of 2002es-like SNe Ia. 

   more » « less
2. SN 2023zcu: A Type IIP SN with Early Flash Features

   https://doi.org/10.3847/1538-4357/ae3c7e  

   Dubey, Monalisa; Misra, Kuntal; Csörnyei, Géza; Dastidar, Raya; Howell, D Andrew; Sand, David J; Valenti, Stefano; Zheng, WeiKang; Filippenko, Alexei V; Jha, Saurabh; et al (February 2026, The Astrophysical Journal)

   Abstract We present a detailed photometric and spectroscopic analysis of the Type IIP supernova (SN) SN 2023zcu, which exploded in the galaxy NGC 2139 (redshiftz= 0.006). SN 2023zcu exhibits a well-sampled light curve covering the rise, plateau, and nebular phases. It has an optically thick phase of 100.6  ±  0.6 days with a magnitude drop of ∼1.7 mag in theVband during the transition between the plateau and nebular phases. Weak emission features in the early-time spectra indicate a low-level interaction between circumstellar material and the SN ejecta. The spectral evolution is well sampled and exhibits a prominent P Cygni profile of Hα, a defining characteristic of Type IIP SNe. Signatures of metal-line formation (e.g., Feii, Caiinear-infrared triplet) are also evident in the spectra as the SN evolves. Spectral modeling with the radiative transfer codeTARDISduring the early photospheric phase (8.7–35.5 days since explosion) yields photospheric temperatures decreasing from ∼9000 to ∼6000 K and expansion velocities declining from ∼10,000 to ∼5400 km s⁻¹. A tailored expanding photosphere method fit based on theTARDISmodels provides a distance estimate of 27.8  ±  2.0 Mpc. Nebular-phase spectra and bolometric light-curve modeling suggest a progenitor mass in the range 12–15M_⊙. This thorough analysis helps to constrain progenitor properties and explosion parameters, thereby strengthening our understanding of Type IIP SNe. 

   more » « less
3. Low-luminosity Type IIP Supernovae from the Zwicky Transient Facility Census of the Local Universe. III. Hunting for Electron-capture Supernovae Using Nebular Spectroscopy

   https://doi.org/10.1088/1538-3873/ae7daf  

   Das, Kaustav K; Jerkstrand, Anders; Kasliwal, Mansi M; Sollerman, Jesper; Fremling, Christoffer; Schulze, Steve; Gal-Yam, Avishay; Ahumuda, Tomas; Anand, Shreya; van_Baal, Bart; et al (July 2026, Publications of the Astronomical Society of the Pacific)

   Abstract Electron-capture supernovae (ECSNe) may arise from ONeMg-core collapse in super-asymptotic giant branch (sAGB) stars near the low-mass core-collapse limit (≈8–10M_⊙). At early times, models predict that ECSNe resemble low-mass red supergiant iron-core-collapse SNe, making the two channels difficult to distinguish. Nebular spectroscopy, however, can reveal differences in ejecta composition. We present a systematic sample of 19 nebular spectra of low-luminosity Type IIP (LLIIP) SNe from the Zwicky Transient Facility Census of the Local Universe survey, obtained 115−450 days after explosion. Their low velocities expose narrow lines blended in brighter SNe, which we identify and model to constrain progenitor properties. We find a strong correlation between the FWHM of Hiλ6563 and peak luminosity, showing that LLIIP SNe occupy the low-energy end of the core-collapse population, but no correlation with plateau duration, suggesting that envelope and core properties are not tightly linked. Only one SN reaches the extremely low Hiλ6563 widths predicted for the weakest ∼9M_⊙explosion models, implying that such low-energy events are intrinsically rare. Combining our sample with 118 literature nebular spectra of Type II SNe, we infer an IMF slope of 2.1 ± 1.2. We also introduce an “ECSN score” based on the absence of He- and O-shell emission lines, and identify two plausible ECSN candidates, SN 2023bvj and SN 2024btj. However, neither shows the extremely narrow nebular lines predicted by current ECSN models. If ECSNe arise predominantly through the LLIIP channel, we infer an upper limit on the ECSN rate of ≲(5–8) × 10²Gpc⁻³yr⁻¹, corresponding to a narrow sAGB progenitor mass window of ΔM_sAGB ≲ 0.02–0.06M_⊙. 

   more » « less
4. Type Ia supernovae in the age of JWST: Finding the ‘right’ questions and the path to answers

   https://doi.org/10.1088/1742-6596/2742/1/012024  

   Hoeflich, Peter; Fereidouni, Elham; Mera, Tyco Brahe (April 2024, Journal of Physics: Conference Series)

   Abstract Understanding the Physics of thermonuclear explosions of a White Dwarf star (WD), so called Type Ia Supernovae (SNe Ia), provide a playground for modern physics, computational methods, and are a key to modern cosmology. We identify new and investigate a variety of observational signatures of underlying physical processes related to the thermonuclear runaway, the flame propagation and the environment. Being intrinsically multi-dimensional phenomena, probing the physics requires multi-dimensional radiation-hydrodynamics and MHD simulations. For this task, we developed and employed methods for photon transport for the X-, gamma- and of low energy and of positrons under non-LTE conditions. We identify signatures in the light curves and spectra, in particular, line profiles and polarization spectra. Consistent treatment of high energy processes is critical. Therefore, our framework and results can be used directly a variety of scenarios for SNe Ia including merging WDs and explosions of sub-Chandrasekhar mass WDs. Current simulations have limitations but, nevertheless, when combined with recent JWST and VLT observations solutions emerge to many of decade old problems on the ignition process, flame physics and thermonuclear explosion. 

   more » « less
5. JWST Low-resolution MIRI Spectral Observations of SN 2021aefx: High-density Burning in a Type Ia Supernova

   https://doi.org/10.3847/2041-8213/acb8a8  

   DerKacy, J. M.; Ashall, C.; Hoeflich, P.; Baron, E.; Shappee, B. J.; Baade, D.; Andrews, J.; Bostroem, K. A.; Brown, P. J.; Burns, C. R.; et al (February 2023, The Astrophysical Journal Letters)

   Abstract We present a JWST/MIRI low-resolution mid-infrared (MIR) spectroscopic observation of the normal Type Ia supernova (SN Ia) SN 2021aefx at +323 days past rest-frameB-band maximum light. The spectrum ranges from 4 to 14μm and shows many unique qualities, including a flat-topped [Ariii] 8.991μm profile, a strongly tilted [Coiii] 11.888μm feature, and multiple stable Ni lines. These features provide critical information about the physics of the explosion. The observations are compared to synthetic spectra from detailed non–local thermodynamic equilibrium multidimensional models. The results of the best-fitting model are used to identify the components of the spectral blends and provide a quantitative comparison to the explosion physics. Emission line profiles and the presence of electron capture elements are used to constrain the mass of the exploding white dwarf (WD) and the chemical asymmetries in the ejecta. We show that the observations of SN 2021aefx are consistent with an off-center delayed detonation explosion of a near–Chandrasekhar mass (M_Ch) WD at a viewing angle of −30° relative to the point of the deflagration to detonation transition. From the strengths of the stable Ni lines, we determine that there is little to no mixing in the central regions of the ejecta. Based on both the presence of stable Ni and the Ar velocity distributions, we obtain a strict lower limit of 1.2M_⊙for the initial WD, implying that most sub-M_Chexplosions models are not viable models for SN 2021aefx. The analysis here shows the crucial importance of MIR spectra in distinguishing between explosion scenarios for SNe Ia. 

   more » « less