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1. An Infrared Echo from a Circumstellar Disk in the Hydrogen- and Helium-poor SN 2024aecx

   https://doi.org/10.3847/1538-4357/ae623e  

   Tinyanont, Samaporn; Wangnok, Kittipong; Andrews, Jennifer E; Foley, Ryan J; Kaewmookda, Methawee; Jencson, Jacob E; Rest, Armin; Auchettl, Katie; Bostroem, K Azalee; Coulter, David A; et al (June 2026, The Astrophysical Journal)

   Abstract We present near-infrared (NIR) spectroscopy of the hydrogen- and helium-poor (Type Ic supernovae (SNe Ic)) SN 2024aecx, which displays a strong NIR excess emerging 32 days postpeak. SN 2024aecx is a peculiar SN Ic that exhibited luminous shock-cooling emission at early times, suggestive of close-in circumstellar medium (CSM), unexpected for this class of supernovae (SNe). Its early NIR spectra are typical for a SNe Ic but with strong Ciabsorption features. By ∼32 days postpeak, the spectra show a strong NIR excess, while maintaining normal optical colors, unprecedented for SNe Ic. We find that the NIR excess is well fit with a single-temperature, optically thin dust model with declining temperature, increasing mass, and roughly constant luminosity over time. The NIR excess appears too promptly for dust to have formed in the supernova (SN) ejecta, indicating an IR echo from preexisting dust in the CSM. The IR echo is likely powered by the relatively slowly evolving SN peak light, and not the brief shock cooling emission, as the latter requires unrealistically high CSM densities to explain the observed dust mass. We consider different potential CSM geometries and find that a thick face-on disk with an inner edge of around 5 × 10¹⁶cm can best explain the dust mass and temperature evolution. In this scenario, the SN shock should start interacting with this CSM 440 ± 200 days postexplosion. CSM around SNe Ic is rare, and follow-up observations of SN 2024aecx will probe the mass-loss process responsible for removing hydrogen and helium from its progenitor star. 

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2. Very Late-time JWST and Keck Spectra of the Oxygen-rich Supernova 1995N

   https://doi.org/10.3847/1538-4357/adfc72  

   Clayton, Geoffrey C; Wesson, R; Fox, Ori D; Shahbandeh, Melissa; Filippenko, Alexei V; Nickson, Bryony; Engesser, Michael; Van_Dyk, Schuyler D; Zheng, WeiKang; Brink, Thomas G; et al (September 2025, The Astrophysical Journal)

   Abstract We present new JWST/MIRI Medium Resolution Spectroscopy and Keck spectra of SN 1995N obtained in 2022–2023, more than 10,000 days after the supernova (SN) explosion. These spectra are among the latest direct detections of a core-collapse SN, both through emission lines in the optical and thermal continuum from infrared (IR) dust emission. The new IR data show that dust heating from radiation produced by the ejecta interacting with circumstellar matter is still present but greatly reduced from when SN 1995N was observed by the Spitzer Space Telescope and WISE in 2009/2010 and 2018, when the dust mass was estimated to be 0.4M_⊙. New radiative-transfer modeling suggests that the dust mass and grain size may have increased between 2010 and 2023. The new data can alternatively be well fit with a dust mass of 0.4M_⊙and a much reduced heating source luminosity. The new late-time spectra show unusually strong oxygen forbidden lines, stronger than the Hαemission. This indicates that SN 1995N may have exploded as a stripped-envelope SN, which then interacted with a massive H-rich circumstellar shell, changing it from intrinsically Type Ib/c to Type IIn. The late-time spectrum results when the reverse shock begins to excite the inner H-poor, O-rich ejecta. This change in the spectrum is rarely seen but marks the start of the transition from SN to SN remnant. 

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3. A Panchromatic View of Late-time Shock Power in the Type II Supernova 2023ixf

   https://doi.org/10.3847/2041-8213/ae157a  

   Jacobson-Galán, W V; Dessart, L; Kilpatrick, C D; Patel, P J; Auchettl, K; Tinyanont, S; Margutti, R; Dwarkadas, V V; Bostroem, K A; Chornock, R; et al (November 2025, The Astrophysical Journal Letters)

   Abstract 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 ∼0.1–30μm. 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 $\dot{M}\approx 10^{-4}$ M_⊙yr⁻¹(v_w = 20 ± 5 km s⁻¹). Additionally, we construct multiepoch spectral models from the non-LTE radiative transfer codeCMFGENthat contain radioactive decay and shock powers as well as dust absorption, scattering, and emission. We find that models with shock powers ofL_sh = (0.5–1) × 10⁴⁰erg s⁻¹and ∼(0.5–1) × 10⁻³M_⊙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. 

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4. SN 2022oqm: A Bright and Multipeaked Calcium-rich Transient

   https://doi.org/10.3847/1538-4357/ad5a7c  

   Yadavalli, S Karthik; Villar, V Ashley; Izzo, Luca; Zenati, Yossef; Foley, Ryan J; Wheeler, J Craig; Angus, Charlotte R; Bánhidi, Dominik; Auchettl, Katie; Bíró, Barna Imre; et al (September 2024, The Astrophysical Journal)

   Abstract We present the photometric and spectroscopic evolution of SN 2022oqm, a nearby multipeaked hydrogen- and helium-weak calcium-rich transient (CaRT). SN 2022oqm was detected 13.1 kpc from its host galaxy, the face-on spiral galaxy NGC 5875. Extensive spectroscopic coverage reveals an early hot (T≥ 40,000 K) continuum and carbon features observed ∼1 day after discovery, SN Ic-like photospheric-phase spectra, and strong forbidden calcium emission starting 38 days after discovery. SN 2022oqm has a relatively high peak luminosity (M_B= −17 mag) for CaRTs, making it an outlier in the population. We determine that three power sources are necessary to explain the light curve (LC), with each corresponding to a distinct peak. The first peak is powered by an expanding blackbody with a power-law luminosity, suggesting shock cooling by circumstellar material (CSM). Subsequent LC evolution is powered by a double radioactive decay model, consistent with two sources of photons diffusing through optically thick ejecta. From the LC, we derive an ejecta mass and⁵⁶Ni mass of ∼0.6M_⊙and ∼0.09M_⊙. Spectroscopic modeling ∼0.6M_⊙of ejecta, and with well-mixed Fe-peak elements throughout. We discuss several physical origins for SN 2022oqm and find either a surprisingly massive white dwarf progenitor or a peculiar stripped envelope model could explain SN 2022oqm. A stripped envelope explosion inside a dense, hydrogen- and helium-poor CSM, akin to SNe Icn, but with a large 56Ni mass and small CSM mass could explain SN 2022oqm. Alternatively, helium detonation on an unexpectedly massive white dwarf could also explain SN 2022oqm. 

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5. SN 2022oqm–A Ca-rich Explosion of a Compact Progenitor Embedded in C/O Circumstellar Material

   https://doi.org/10.3847/1538-4357/ad04d7  

   Irani, Ido; Chen, Ping; Morag, Jonathan; Schulze, Steve; Gal-Yam, Avishay; Strotjohann, Nora L; Yaron, Ofer; Zimmerman, Erez A; Sharon, Amir; Perley, Daniel A; et al (February 2024, The Astrophysical Journal)

   Abstract We present the discovery and analysis of SN 2022oqm, a Type Ic supernova (SN) detected <1 day after the explosion. The SN rises to a blue and short-lived (2 days) initial peak. Early-time spectral observations of SN 2022oqm show a hot (40,000 K) continuum with high ionization C and O absorption features at velocities of 4000 km s⁻¹, while its photospheric radius expands at 20,000 km s⁻¹, indicating a pre-existing distribution of expanding C/O material. After ∼2.5 days, both the spectrum and light curves evolve into those of a typical SN Ic, with line velocities of ∼10,000 km s⁻¹, in agreement with the evolution of the photospheric radius. The optical light curves reach a second peak att≈ 15 days. Byt= 60 days, the spectrum of SN 2022oqm becomes nearly nebular, displaying strong Caiiand [Caii] emission with no detectable [Oi], marking this event as Ca-rich. The early behavior can be explained by 10⁻³M_⊙of optically thin circumstellar material (CSM) surrounding either (1) a massive compact progenitor such as a Wolf–Rayet star, (2) a massive stripped progenitor with an extended envelope, or (3) a binary system with a white dwarf. We propose that the early-time light curve is powered by both the interaction of the ejecta with the optically thin CSM and shock cooling (in the massive star scenario). The observations can be explained by CSM that is optically thick to X-ray photons, is optically thick in the lines as seen in the spectra, and is optically thin to visible-light continuum photons that come either from downscattered X-rays or from the shock-heated ejecta. Calculations show that this scenario is self-consistent. 

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