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1. The Extremely Metal-poor SN 2023ufx: A Local Analog to High-redshift Type II Supernovae

   https://doi.org/10.3847/1538-4357/ad8448  

   Tucker, Michael A; Hinkle, Jason; Angus, Charlotte R; Auchettl, Katie; Hoogendam, Willem B; Shappee, Benjamin; Kochanek, Christopher S; Ashall, Chris; de_Boer, Thomas; Chambers, Kenneth C; et al (November 2024, The Astrophysical Journal)

   Abstract We present extensive observations of the Type II supernova (SN II) SN 2023ufx, which is likely the most metal-poor SN II observed to date. It exploded in the outskirts of a low-metallicity (Z_host∼ 0.1Z_⊙) dwarf (M_g= −13.39 ± 0.16 mag,r_proj∼ 1 kpc) galaxy. The explosion is luminous, peaking atM_g≈ −18.5 mag, and shows rapid evolution. Ther-band (pseudobolometric) light curve has a shock-cooling phase lasting 20 (17) days followed by a 19 (23) day plateau. The entire optically thick phase lasts only ≈55 days following explosion, indicating that the red supergiant progenitor had a thinned H envelope prior to explosion. The early spectra obtained during the shock-cooling phase show no evidence for narrow emission features and limit the preexplosion mass-loss rate to $\dot{M}\lesssim {10}^{-3}$M_⊙yr⁻¹. The photospheric-phase spectra are devoid of prominent metal absorption features, indicating a progenitor metallicity of ≲0.1Z_⊙. The seminebular (∼60–130 days) spectra reveal weak Feii, but other metal species typically observed at these phases (Tiii, Scii, and Baii) are conspicuously absent. The late-phase optical and near-infrared spectra also reveal broad (≈10⁴km s⁻¹) double-peaked Hα, Pβ, and Pγemission profiles suggestive of a fast outflow launched during the explosion. Outflows are typically attributed to rapidly rotating progenitors, which also prefer metal-poor environments. This is only the second SN II with ≲0.1Z_⊙and both exhibit peculiar evolution, suggesting a sizable fraction of metal-poor SNe II have distinct properties compared to nearby metal-enriched SNe II. These observations lay the groundwork for modeling the metal-poor SNe II expected in the early Universe. 

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2. SN 2021tsz: A luminous, short photospheric phase Type II supernova in a low-metallicity host

   https://doi.org/10.1051/0004-6361/202556058  

   Dastidar, R; Pignata, G; Dukiya, N; Misra, K; Howell, D A; Singh, M; Gutiérrez, C P; Pellegrino, C; Kumar, A; Ayala, B; et al (November 2025, Astronomy & Astrophysics)

   We present the analysis of the luminous Type II Supernova (SN) 2021tsz, which exploded in a low-luminosity galaxy. It reached a peak magnitude of −18.88 ± 0.13 mag in therband and exhibited an initial rapid decline of 4.05 ± 0.14 mag (100 d)⁻¹from peak luminosity till ∼30 d. The photospheric phase is short, with the SN displaying bluer colours and a weak Hαabsorption component–features consistent with other luminous, short-photospheric phase Type II SNe. A distinct transition from the photospheric to the radioactive tail phase in theVband–as is common in hydrogen-rich Type II SNe–is not visible in SN 2021tsz, although a modest ∼1 mag drop is apparent in the redder filters. Hydrodynamic modelling suggests the luminosity is powered by ejecta-circumstellar material (CSM) interaction during the early phases (< 30 days). Interaction with 0.6 M_⊙of dense CSM extending to 3100 R_⊙reproduces the observed luminosity, with an explosion energy of 1.3 × 10⁵¹erg. The modelling indicates a pre-SN mass of 9 M_⊙, which includes a hydrogen envelope of 4 M_⊙, and a radius of ∼1000 R_⊙. Spectral energy distribution analysis and strong-line diagnostics revealed that the host galaxy of SN 2021tsz is a low-metallicity, dwarf galaxy. The low-metallicity environment and the derived high mass loss from the hydrodynamical modelling strongly support a binary progenitor system for SN 2021tsz. 

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3. SN 2018is: A low-luminosity Type IIP supernova with narrow hydrogen emission lines at early phases

   https://doi.org/10.1051/0004-6361/202452507  

   Dastidar, R; Misra, K; Valenti, S; Sand, D J; Pastorello, A; Reguitti, A; Pignata, G; Benetti, S; Bose, S; Gangopadhyay, A; et al (February 2025, Astronomy & Astrophysics)

   We present a comprehensive photometric and spectroscopic study of the Type IIP supernova (SN) 2018is. TheVband luminosity and the expansion velocity at 50 days post-explosion are −15.1 ± 0.2 mag (corrected for A_V= 1.34 mag) and 1400 km s⁻¹, classifying it as a low-luminosity SN II. The recombination phase in theVband is shorter, lasting around 110 days, and exhibits a steeper decline (1.0 mag per 100 days) compared to most other low-luminosity SNe II. Additionally, the optical and near-infrared spectra display hydrogen emission lines that are strikingly narrow, even for this class. The Fe IIand Sc IIline velocities are at the lower end of the typical range for low-luminosity SNe II. Semi-analytical modelling of the bolometric light curve suggests an ejecta mass of ∼8 M_⊙, corresponding to a pre-supernova mass of ∼9.5 M_⊙, and an explosion energy of ∼0.40 × 10⁵¹erg. Hydrodynamical modelling further indicates that the progenitor had a zero-age main sequence mass of 9 M_⊙, coupled with a low explosion energy of 0.19 × 10⁵¹erg. The nebular spectrum reveals weak [O I]λλ6300,6364 lines, consistent with a moderate-mass progenitor, while features typical of Fe core-collapse events, such as He I, [C I], and Fe I, are indiscernible. However, the redder colours and low ratio of Ni to Fe abundance do not support an electron-capture scenario either. As a low-luminosity SN II with an atypically steep decline during the photospheric phase and remarkably narrow emission lines, SN 2018is contributes to the diversity observed within this population. 

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4. SN 2022jox: An Extraordinarily Ordinary Type II SN with Flash Spectroscopy

   https://doi.org/10.3847/1538-4357/ad2a49  

   Andrews, Jennifer E; Pearson, Jeniveve; Hosseinzadeh, Griffin; Bostroem, K Azalee; Dong_董, Yize 一泽; Shrestha, Manisha; Jencson, Jacob E; Sand, David J; Valenti, S; Hoang, Emily; et al (April 2024, The Astrophysical Journal)

   Abstract We present high-cadence optical and ultraviolet (UV) observations of the Type II supernova (SN), SN 2022jox which exhibits early spectroscopic high-ionization flash features of Hi, Heii, Civ, and Nivthat disappear within the first few days after explosion. SN 2022jox was discovered by the Distance Less Than 40 Mpc survey ∼0.75 day after explosion with follow-up spectra and UV photometry obtained within minutes of discovery. The SN reached a peak brightness ofM_V∼ −17.3 mag, and has an estimated⁵⁶Ni mass of 0.04M_⊙, typical values for normal Type II SNe. The modeling of the early light curve and the strong flash signatures present in the optical spectra indicate interaction with circumstellar material (CSM) created from a progenitor with a mass-loss rate of $\dot{M}\sim {10}^{-3}\text{–}{10}^{-2}{M}_{\odot }{\mathrm{y}\mathrm{r}}^{-1}$. There may also be some indication of late-time CSM interaction in the form of an emission line blueward of Hαseen in spectra around 200 days. The mass-loss rate of SN 2022jox is much higher than the values typically associated with quiescent mass loss from red supergiants, the known progenitors of Type II SNe, but is comparable to inferred values from similar core-collapse SNe with flash features, suggesting an eruptive event or a superwind in the progenitor in the months or years before explosion. 

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5. Massive stars exploding in a He-rich circumstellar medium: XI. Diverse evolution of five Ibn SNe 2020nxt, 2020taz, 2021bbv, 2023utc, and 2024aej

   https://doi.org/10.1051/0004-6361/202554768  

   Wang, Z-Y; Pastorello, A; Cai, Y-Z; Fraser, M; Reguitti, A; Lin, W-L; Tartaglia, L; Andrew_Howell, D; Benetti, S; Cappellaro, E; et al (August 2025, Astronomy & Astrophysics)

   We present the photometric and spectroscopic analysis of five Type Ibn supernovae (SNe): SN 2020nxt, SN 2020taz, SN 2021bbv, SN 2023utc, and SN 2024aej. These events share key observational features and belong to a family of objects similar to the prototypical Type Ibn SN 2006jc. The SNe exhibit rise times of approximately 10 days and peak absolute magnitudes ranging from −16.5 to −19 mag. Notably, SN 2023utc is the faintest Type Ibn SN discovered to date, with an exceptionally lowr-band absolute magnitude of −16.4 mag. The pseudo-bolometric light curves peak at (1 − 10)×10⁴²erg s⁻¹, with total radiated energies on the order of (1 − 10)×10⁴⁸erg. Spectroscopically, these SNe display a relatively slow spectral evolution. The early spectra are characterised by a hot blue continuum and prominent He Iemission lines. The early spectra also show blackbody temperatures exceeding 10 000 K, with a subsequent decline in temperature during later phases. Narrow He Ilines, which are indicative of unshocked circumstellar material (CSM), show velocities of approximately 1000 km s⁻¹. The spectra suggest that the progenitors of these SNe underwent significant mass loss prior to the explosion, resulting in a He-rich CSM. Our light curve modelling yielded estimates for the ejecta mass (M_ej) in the range 1 − 3 M_⊙with kinetic energies (E_Kin) of (0.1 − 1)×10⁵⁰erg. The inferred CSM mass ranges from 0.2 to 1 M_⊙. These findings are consistent with expectations for core collapse events arising from relatively massive envelope-stripped progenitors. 

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