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1. Characterization of Type Ibn Supernovae

   https://doi.org/10.1051/0004-6361/202555954  

   Farias, D; Gall, C; Villar, V A; Auchettl, K; de_Soto, K M; Gagliano, A; Hoogendam, W B; Narayan, G; Sedgewick, A; Yadavalli, S K; et al (April 2026, Astronomy & Astrophysics)

   Context. Type Ibn supernovae (SNe) are characterized by narrow helium (He I) lines from photons produced by the unshocked circumstellar material (CSM). About 80 SNe Ibn have been discovered to date and only a handful of them have extensive observational records. Thus, many open questions remain regarding the progenitor system and the origin of CSM. Aims. Here, we investigate potential correlations between the spectral features of the prominent He Iλ5876 Å line and the optical and X-ray light curve properties of Type Ibn SNe (SNe Ibn). Methods. We compiled the largest sample of 61 SNe Ibn to date, of which 24 SNe have photometric and spectroscopic data available from the Young Supernova Experiment and 37 SNe benefit from archival datasets. We fit 24 SNe Ibn with sufficient photometric coverage (Btozbands) using semi-analytical models fromMOSFiT. Results. We demonstrate that the light curves of SNe Ibn are more diverse than previous analyses suggest, with absoluter-band peak magnitudes (r_max) of −19.4 ± 0.6 mag, along with rise (from −10 days to peak,γ₋₁₀) and decay rates (from peak to +10 days;γ₊₁₀) of −0.08 ± 0.06 and 0.08 ± 0.03 mag/day, respectively. We find that the majority of SNe Ibn in the subsample are consistent with a low-energy explosion (< 10⁵¹erg) of a star with a compact envelope surrounded by ~0.1 M_⊙of helium-rich CSM. The inferred ejecta masses are small (M_ej~ 1 M_⊙) and expand with a velocity of ~5000 km/s. Our spectroscopic analysis shows that the mean velocity of the narrow component of the He Ilines, associated with the CSM, peaks at ~1100 km/s. Conclusions. The mean CSM and ejecta masses inferred for a subsample of SNe Ibn indicate that their progenitors are not massive (~10 M_⊙) single stars at the moment of explosion; rather, they are likely to be binary systems. This finding is in agreement with detections of potential companion stars of SNe Ibn progenitors and inferred CSM properties from stellar evolution models. 

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2. Final Moments. III. Explosion Properties and Progenitor Constraints of CSM-interacting Type II Supernovae

   https://doi.org/10.3847/1538-4357/adfa23  

   Jacobson-Galán, W V; Dessart, L; Davis, K W; Bostroem, K A; Kilpatrick, C D; Margutti, R; Filippenko, A V; Foley, R J; Chornock, R; Terreran, G; et al (October 2025, The Astrophysical Journal)

   Abstract We present analysis of the plateau and late-time phase properties of a sample of 39 Type II supernovae (SNe II) that show narrow, transient, high-ionization emission lines (i.e., “IIn-like”) in their early-time spectra from interaction with confined, dense circumstellar material (CSM). Originally presented by W. V. Jacobson-Galán et al., this sample also includes multicolor light curves and spectra extending to late-time phases of 35 SNe with no evidence for IIn-like features at <2 days after first light. We measure photospheric phase light-curve properties for the distance-corrected sample and find that SNe II with IIn-like features have significantly higher luminosities and decline rates at +50 days than the comparison sample, which could be connected to inflated progenitor radii, lower ejecta mass, and/or persistent CSM interaction. However, we find no statistical evidence that the measured plateau durations and⁵⁶Ni masses of SNe II with and without IIn-like features arise from different distributions. We estimate progenitor zero-age main-sequence (ZAMS) masses for all SNe with nebular spectroscopy through spectral model comparisons and find that most objects, both with and without IIn-like features, are consistent with progenitor masses ≤12.5M_⊙. Combining progenitor ZAMS masses with CSM densities inferred from early-time spectra suggests multiple channels for enhanced mass loss in the final years before core collapse, such as a convection-driven chromosphere or binary interaction. Finally, we find spectroscopic evidence for ongoing ejecta-CSM interaction at radii >10¹⁶cm, consistent with substantial progenitor mass-loss rates of ∼10⁻⁴–10⁻⁵M_⊙yr⁻¹(v_w < 50 km s⁻¹) in the final centuries to millennia before explosion. 

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3. The New Status Qvo? SN 2021qvo Is Another 2003fg-like Type Ia Supernova with a Rising Light-curve Bump

   https://doi.org/10.3847/1538-4357/ae279b  

   Paniagua, I_A Abreu; Hoogendam, W B; Jones, D O; Dimitriadis, G; Foley, R J; Gall, C; O’Brien, J; Taggart, K; Angus, C R; Ashall, C; et al (January 2026, The Astrophysical Journal)

   Abstract In recent years, multiple Type Ia supernovae (SNe Ia) have been observed with “bumps” in their rising light curves shortly after the explosion. Here, we present SN 2021qvo: an SN Ia that exhibits a clear early bump in photometry obtained by the Young Supernova Experiment. Photometric and spectroscopic observations of SN 2021qvo show that it has a broader light curve, higher peak luminosity, shallower Siiiλ5972 pseudoequivalent width, and lower ejecta velocities than normal SNe Ia, which are all consistent with the characteristics of the 2003fg-like (often called “super-Chandrasekhar”) SN subtype. Including SN 2021qvo, just four known 2003fg-like SNe Ia have sufficient prepeak data to reveal a rising light-curve bump, and all four have bump detections. A host-galaxy analysis reveals that SN 2021qvo exploded in a low-mass galaxy $\log (M_{*}/M_{\odot })=7.83_{-0.24}^{+0.17}$, also consistent with other members of this class. The current leading early bump 2003fg-like SN Ia progenitor model involves an interaction between the circumstellar material (CSM) and the SN ejecta. We test the validity of this theory by modeling the early bump and subsequent light-curve evolution of SN 2021qvo with the Modular Open Source Fitter for Transients. We find that the bump can be modeled with a best-fit CSM mass in the rangeM_CSM= 3.31−8.51 × 10⁻³M_⊙. SN 2021qvo adds to the small but growing number of 2003fg-like SNe Ia with rising light-curve bumps; as the number of these SNe Ia with CSM estimates continues to grow, population-level inferences about the CSM distribution will be able to constrain the progenitor scenario for these SNe Ia. 

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4. JWST Spectroscopy of SNe Ia 2022aaiq and 2024gy: Evidence for Enhanced Central Stable Ni Abundance and a Deflagration-to-detonation Transition

   https://doi.org/10.3847/1538-4357/ae6867  

   Kwok, Lindsey A; Liu_刘, Chang 畅; Jha, Saurabh W; Blondin, Stéphane; Larison, Conor; Miller, Adam A; Dai, Mi; Foley, Ryan J; Filippenko, Alexei V; Andrews, Jennifer E; et al (June 2026, The Astrophysical Journal)

   Abstract 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 0.35–28μm. Medium-resolution JWST spectroscopy reveals novel narrow (v_FWHM < 1500 km s⁻¹) [Niii] 1.94 and 6.64μm cores in both events. The MIR [Niii] 6.64 μm 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_Chprogenitor. 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 [Niiii] 7.35 μm 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_Chscenario for SN 2024gy and a sub-M_Chscenario 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. 

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5. A Physical Basis for the H-band Blue-edge Velocity and Light-curve Shape Correlation in Context of Type Ia Supernova Explosion Physics

   https://doi.org/https://ui.adsabs.harvard.edu/link_gateway/2019ApJ...878...86A/doi:10.3847/1538-4357/ab204b  

   C. Ashall, 1 P. (July 2019, The Astrophysical journal)

   Our recent work demonstrates a correlation between the high-velocity blue edge, vedge, of the ironpeak Fe/Co/Ni H-band emission feature and the optical light curve shape of normal, transitional and sub-luminous type Ia Supernovae (SNe Ia). We explain this correlation in terms of SN Ia physics. vedge corresponds to the sharp transition between the complete and incomplete silicon burning regions in the ejecta. It measures the point in velocity space where the outer 56Ni mass fraction, XNi, falls to the order of 0.03-0.10. For a given 56Ni mass, M(56Ni), vedge is sensitive to the speci c kinetic energy Ekin(M(56Ni)=MWD) of the corresponding region. Combining vedge with light curve parameters (i.e., sBV ,
   m15;s in B and V ) allows us to distinguish between explosion scenarios. The correlation between vedge and light-curve shape is consistent with explosion models near the Chandrasekhar limit. However, the available sub-MCh WD explosion model based on SN 1999by exhibits velocities which are too large to explain the observations. Finally, the sub-luminous SN 2015bo exhibits signatures of a dynamical merger of two WDs demonstrating diversity among explosion scenarios at the faint end of the SNe Ia population. 

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