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1. Ground-based and JWST Observations of SN 2022pul. I. Unusual Signatures of Carbon, Oxygen, and Circumstellar Interaction in a Peculiar Type Ia Supernova

   https://doi.org/10.3847/1538-4357/ad0975  

   Siebert, Matthew R; Kwok, Lindsey A; Johansson, Joel; Jha, Saurabh W; Blondin, Stéphane; Dessart, Luc; Foley, Ryan J; Hillier, D John; Larison, Conor; Pakmor, Rüdiger; et al (December 2023, The Astrophysical Journal)

   Abstract Nebular-phase observations of peculiar Type Ia supernovae (SNe Ia) provide important constraints on progenitor scenarios and explosion dynamics for both these rare SNe and the more common, cosmologically useful SNe Ia. We present observations from an extensive ground- and space-based follow-up campaign to characterize SN 2022pul, a super-Chandrasekhar mass SN Ia (alternatively “03fg-like” SN), from before peak brightness to well into the nebular phase across optical to mid-infrared (MIR) wavelengths. The early rise of the light curve is atypical, exhibiting two distinct components, consistent with SN Ia ejecta interacting with dense carbon–oxygen (C/O)-rich circumstellar material (CSM). In the optical, SN 2022pul is most similar to SN 2012dn, having a low estimated peak luminosity (M_B= −18.9 mag) and high photospheric velocity relative to other 03fg-like SNe. In the nebular phase, SN 2022pul adds to the increasing diversity of the 03fg-like subclass. From 168 to 336 days after peakB-band brightness, SN 2022pul exhibits asymmetric and narrow emission from [Oi]λλ6300, 6364 (FWHM ≈ 2000 km s⁻¹), strong, broad emission from [Caii]λλ7291, 7323 (FWHM ≈ 7300 km s⁻¹), and a rapid Feiiito Feiiionization change. Finally, we present the first ever optical-to-MIR nebular spectrum of an 03fg-like SN Ia using data from JWST. In the MIR, strong lines of neon and argon, weak emission from stable nickel, and strong thermal dust emission (withT≈ 500 K), combined with prominent [Oi] in the optical, suggest that SN 2022pul was produced by a white dwarf merger within C/O-rich CSM. 

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2. The Type Ibn Supernova 2019kbj: Indications for Diversity in Type Ibn Supernova Progenitors

   https://doi.org/10.3847/1538-4357/acb432  

   Ben-Ami, Tom; Arcavi, Iair; Newsome, Megan; Farah, Joseph; Pellegrino, Craig; Terreran, Giacomo; Burke, Jamison; Hosseinzadeh, Griffin; McCully, Curtis; Hiramatsu, Daichi; et al (March 2023, The Astrophysical Journal)

   Abstract Type Ibn supernovae (SNe) are a rare class of stellar explosions whose progenitor systems are not yet well determined. We present and analyze observations of the Type Ibn SN 2019kbj, and model its light curve in order to constrain its progenitor and explosion parameters. SN 2019kbj shows roughly constant temperature during the first month after peak, indicating a power source (likely circumstellar material interaction) that keeps the continuum emission hot at ∼15,000 K. Indeed, we find that the radioactive decay of⁵⁶Ni is disfavored as the sole power source of the bolometric light curve. A radioactive decay + circumstellar material (CSM) interaction model, on the other hand, does reproduce the bolometric emission well. The fits prefer a uniform-density CSM shell rather than CSM due to a steady mass-loss wind, similar to what is seen in other Type Ibn SNe. The uniform-density CSM shell model requires ∼0.1M_⊙of⁵⁶Ni and ∼1M_⊙total ejecta mass to reproduce the light curve. SN 2019kbj differs in this manner from another Type Ibn SN with derived physical parameters, SN 2019uo, for which an order of magnitude lower⁵⁶Ni mass and larger ejecta mass were derived. This points toward a possible diversity in SN Ibn progenitor systems and explosions. 

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3. Radiative Acceleration of Dense Circumstellar Material in Interacting Supernovae

   https://doi.org/10.3847/1538-4357/acdb71  

   Tsuna, Daichi; Murase, Kohta; Moriya, Takashi J. (July 2023, The Astrophysical Journal)

   Abstract Early-time light curves/spectra of some hydrogen-rich supernovae (SNe) provide solid evidence of the existence of confined, dense circumstellar matter (CSM) surrounding dying massive stars. We numerically and analytically study the radiative acceleration of CSM in such systems, where the radiation is mainly powered by the interaction between the SN ejecta and the CSM. We find that the acceleration of the unshocked dense CSM ahead of the shock is larger for massive and compact CSM, with velocities reaching up to ∼10³km s⁻¹for a CSM of order 0.1M_⊙confined within ∼10¹⁵cm. We show that the dependence of the acceleration on the CSM density helps us explain the diversity of the CSM velocity inferred from the early spectra of some Type II SNe. For explosions in even denser CSM, radiative acceleration can affect the dissipation of strong collisionless shocks formed after the shock breakout, which would affect early nonthermal emission expected from particle acceleration. 

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4. Early Spectroscopy and Dense Circumstellar Medium Interaction in SN 2023ixf

   https://doi.org/10.3847/2041-8213/acf9a4  

   Bostroem, K. Azalee; Pearson, Jeniveve; Shrestha, Manisha; Sand, David J.; Valenti, Stefano; Jha, Saurabh W.; Andrews, Jennifer E.; Smith, Nathan; Terreran, Giacomo; Green, Elizabeth; et al (October 2023, The Astrophysical Journal Letters)

   Abstract We present the optical spectroscopic evolution of SN 2023ixf seen in subnight cadence spectra from 1.18 to 15 days after explosion. We identify high-ionization emission features, signatures of interaction with material surrounding the progenitor star, that fade over the first 7 days, with rapid evolution between spectra observed within the same night. We compare the emission lines present and their relative strength to those of other supernovae with early interaction, finding a close match to SN 2020pni and SN 2017ahn in the first spectrum and SN 2014G at later epochs. To physically interpret our observations, we compare them to CMFGEN models with confined, dense circumstellar material around a red supergiant (RSG) progenitor from the literature. We find that very few models reproduce the blended Niii(λλ4634.0,4640.6)/Ciii(λλ4647.5,4650.0) emission lines observed in the first few spectra and their rapid disappearance thereafter, making this a unique diagnostic. From the best models, we find a mass-loss rate of 10⁻³–10⁻²M_⊙yr⁻¹, which far exceeds the mass-loss rate for any steady wind, especially for an RSG in the initial mass range of the detected progenitor. These mass-loss rates are, however, similar to rates inferred for other supernovae with early circumstellar interaction. Using the phase when the narrow emission features disappear, we calculate an outer dense radius of circumstellar materialR_CSM,out≈ 5 × 10¹⁴cm, and a mean circumstellar material density ofρ= 5.6 × 10⁻¹⁴g cm⁻³. This is consistent with the lower limit on the outer radius of the circumstellar material we calculate from the peak Hαemission flux,R_CSM,out≳ 9 × 10¹³cm. 

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5. The Atacama Cosmology Telescope: Galactic Dust Structure and the Cosmic PAH Background in Cross-correlation with WISE

   https://doi.org/10.3847/1538-4357/ad05cd  

   Córdova Rosado, Rodrigo; Hensley, Brandon S.; Clark, Susan E.; Duivenvoorden, Adriaan J.; Atkins, Zachary; Battistelli, Elia Stefano; Choi, Steve K.; Dunkley, Jo; Hervías-Caimapo, Carlos; Li, Zack; et al (January 2024, The Astrophysical Journal)

   Abstract We present a cross-correlation analysis between $1\prime$resolution total intensity and polarization observations from the Atacama Cosmology Telescope (ACT) at 150 and 220 GHz and 15″ mid-infrared photometry from the Wide-field Infrared Survey Explorer (WISE) over 107 12.°5 × 12.°5 patches of sky. We detect a spatially isotropic signal in the WISE×ACTTTcross-power spectrum at 30σsignificance that we interpret as the correlation between the cosmic infrared background at ACT frequencies and polycyclic aromatic hydrocarbon (PAH) emission from galaxies in WISE, i.e., the cosmic PAH background. Within the Milky Way, the Galactic dustTTspectra are generally well described by power laws inℓover the range 10³<ℓ< 10⁴, but there is evidence both for variability in the power-law index and for non-power-law behavior in some regions. We measure a positive correlation between WISE total intensity and ACTE-mode polarization at 1000 <ℓ≲ 6000 at >3σin each of 35 distinct ∼100 deg²regions of the sky, suggesting that alignment between Galactic density structures and the local magnetic field persists to subparsec physical scales in these regions. The distribution ofTEamplitudes in thisℓrange across all 107 regions is biased to positive values, while there is no evidence for such a bias in theTBspectra. This work constitutes the highest-ℓmeasurements of the Galactic dustTEspectrum to date and indicates that cross-correlation with high-resolution mid-infrared measurements of dust emission is a promising tool for constraining the spatial statistics of dust emission at millimeter wavelengths. 

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