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1. A Comprehensive Optical Search for Pre-explosion Outbursts from the Quiescent Progenitor of SN 2023ixf

   https://doi.org/10.3847/1538-4357/acef18  

   Dong 董, Yize 一泽; Sand, David J.; Valenti, Stefano; Bostroem, K. Azalee; Andrews, Jennifer E.; Hosseinzadeh, Griffin; Hoang, Emily; Janzen, Daryl; Jencson, Jacob E.; Lundquist, Michael; et al (October 2023, The Astrophysical Journal)

   Abstract We perform a comprehensive search for optical precursor emission at the position of SN 2023ixf using data from the DLT40, ZTF, and ATLAS surveys. By comparing the current data set with precursor outburst hydrodynamical model light curves, we find that the probability of a significant outburst within 5 yr of explosion is low, and the circumstellar material (CSM) ejected during any possible precursor outburst is likely smaller than ∼0.015M_⊙. By comparing to a set of toy models, we find that, if there was a precursor outburst, the duration must have been shorter than ∼100 days for a typical brightness ofM_r≃ −9 mag or shorter than 200 days forM_r≃ −8 mag; brighter, longer outbursts would have been discovered. Precursor activity like that observed in the normal Type II SN 2020tlf (M_r≃ −11.5) can be excluded in SN 2023ixf. If the dense CSM inferred by early flash spectroscopy and other studies is related to one or more precursor outbursts, then our observations indicate that any such outburst would have to be faint and only last for days to months, or it occurred more than 5 yr prior to the explosion. Alternatively, any dense, confined CSM may not be due to eruptive mass loss from a single red supergiant progenitor. Taken together, the results of SN 2023ixf and SN 2020tlf indicate that there may be more than one physical mechanism behind the dense CSM inferred around some normal Type II supernovae. 

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2. 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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3. When IIb Ceases To Be: Bridging the Gap between IIb and Short-plateau Supernovae

   https://doi.org/10.3847/1538-4357/ae3a71  

   Farah, Joseph R; Howell, D Andrew; Hiramatsu, Daichi; McCully, Curtis; Andrews, Moira; Newsome, Megan; Padilla_Gonzalez, Estefania; Pellegrino, Craig; Berger, Edo; Blanchard, Peter; et al (February 2026, The Astrophysical Journal)

   Abstract Hydrogen-rich supernovae (SNe) span a range of hydrogen envelope masses at core collapse, producing diverse light curves from extended plateaus in Type IIP SNe to double-peaked Type IIb SNe (SNe IIb). Recent simulations predict a continuous sequence of light-curve morphologies as hydrogen is removed, with short-plateau (SP; plateau durations ≈50–70 days) SNe emerging as a transitional class. However, the observational boundary between types IIb and SP remains poorly defined, and thus far unobserved. We report on extensive photometric and spectroscopic follow-up of SN 2023wdd and SN 2022acrv, two candidate transitional events on the low-mass end of the SP class. Both exhibit weak, double-peaked light curves, which we interpret as exceptionally short plateaus (10–20 days), and hybrid spectral features: persistent Hαabsorption with HeIcontamination, but without the helium dominance characteristic of SNe IIb. Using analytic shock-cooling models and numerical light-curve fitting, we estimate H-rich envelope masses of ∼0.6–0.8M_⊙—significantly larger than canonical IIb values (≲0.1M_⊙) but consistent with the ∼0.9M_⊙threshold predicted for short-plateau behavior. Although the progenitor radii inferred from analytic and numerical methods differ by factors of 2–5, envelope mass estimates are consistent across approaches. Comparisons to well-studied Type IIb (SN 2016gkg, SN 2022hnt), SP (SN 2023ufx, SN 2006ai, SN 2016egz, SN 2006Y), and Type II (SN 2023ixf, SN 2013ej) SNe suggests a monotonic relationship between hydrogen envelope mass and plateau length, consistent with analytic and numerical expectations. These findings provide additional evidence for a continuous distribution of envelope stripping in H-rich core-collapse progenitors, and place SN 2023wdd and SN 2022acrv along the IIb–SP boundary. 

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4. SN 2023ixf in Messier 101: The Twilight Years of the Progenitor as Seen by Pan-STARRS

   https://doi.org/10.3847/1538-4357/ad2df7  

   Ransome, Conor L; Villar, V Ashley; Tartaglia, Anna; Gonzalez, Sebastian Javier; Jacobson-Galán, Wynn V; Kilpatrick, Charles D; Margutti, Raffaella; Foley, Ryan J; Grayling, Matthew; Ni, Yuan Qi; et al (April 2024, The Astrophysical Journal)

   Abstract The nearby type II supernova, SN 2023ixf in M101 exhibits signatures of early time interaction with circumstellar material in the first week postexplosion. This material may be the consequence of prior mass loss suffered by the progenitor, which possibly manifested in the form of a detectable presupernova outburst. We present an analysis of long-baseline preexplosion photometric data in theg,w,r,i,z, andyfilters from Pan-STARRS as part of the Young Supernova Experiment, spanning ∼5000 days. We find no significant detections in the Pan-STARRS preexplosion light curves. We train a multilayer perceptron neural network to classify presupernova outbursts. We find no evidence of eruptive presupernova activity to a limiting absolute magnitude of −7 mag. The limiting magnitudes from the full set ofgwrizy(average absolute magnitude ≈ −8 mag) data are consistent with previous preexplosion studies. We use deep photometry from the literature to constrain the progenitor of SN 2023ixf, finding that these data are consistent with a dusty red supergiant progenitor with luminosity $\log \left(L/L_{\odot }\right)$ ≈ 5.12 and temperature ≈ 3950 K, corresponding to a mass of 14–20M_⊙. 

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5. Circumstellar Interaction in the Ultraviolet Spectra of SN 2023ixf 14–66 Days After Explosion

   https://doi.org/10.3847/2041-8213/ad7855  

   Bostroem, K Azalee; Sand, David J; Dessart, Luc; Smith, Nathan; Jha, Saurabh W; Valenti, Stefano; Andrews, Jennifer E; Dong_董, Yize 一泽; Filippenko, Alexei V; Gomez, Sebastian; et al (September 2024, The Astrophysical Journal Letters)

   Abstract SN 2023ixf was discovered in M101 within a day of the explosion and rapidly classified as a Type II supernova with flash features. Here we present ultraviolet (UV) spectra obtained with the Hubble Space Telescope 14, 19, 24, and 66 days after the explosion. Interaction between the supernova ejecta and circumstellar material (CSM) is seen in the UV throughout our observations in the flux of the first three epochs and asymmetric Mgiiemission on day 66. We compare our observations to CMFGEN supernova models that include CSM interaction ( $\dot{M}<{10}^{-3}$ M_⊙yr⁻¹) and find that the power from CSM interaction is decreasing with time, fromL_sh≈ 5 × 10⁴²erg s⁻¹toL_sh≈ 1 × 10⁴⁰erg s⁻¹between days 14 and 66. We examine the contribution of individual atomic species to the spectra on days 14 and 19, showing that the majority of the features are dominated by iron, nickel, magnesium, and chromium absorption in the ejecta. The UV spectral energy distribution of SN 2023ixf sits between that of supernovae, which show no definitive signs of CSM interaction, and those with persistent signatures assuming the same progenitor radius and metallicity. Finally, we show that the evolution and asymmetric shape of the Mgiiλλ2796, 2802 emission are not unique to SN 2023ixf. These observations add to the early measurements of dense, confined CSM interaction, tracing the mass-loss history of SN 2023ixf to ∼33 yr prior to the explosion and the density profile to a radius of ∼5.7 × 10¹⁵cm. They show the relatively short evolution from a quiescent red supergiant wind to high mass loss. 

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