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1. SN 2022acko: The First Early Far-ultraviolet Spectra of a Type IIP Supernova

   https://doi.org/10.3847/2041-8213/ace31c  

   Bostroem, K. Azalee; Dessart, Luc; Hillier, D. John; Lundquist, Michael; Andrews, Jennifer E.; Sand, David J.; Dong, Yize; Valenti, Stefano; Haislip, Joshua; Hoang, Emily T.; et al (August 2023, The Astrophysical Journal Letters)

   Abstract We present five far- and near-ultraviolet spectra of the Type II plateau supernova, SN 2022acko, obtained 5, 6, 7, 19, and 21 days after explosion, all observed with the Hubble Space Telescope/Space Telescope Imaging Spectrograph. The first three epochs are earlier than any Type II plateau supernova has been observed in the far-ultraviolet revealing unprecedented characteristics. These three spectra are dominated by strong lines, primarily from metals, which contrasts with the featureless early optical spectra. The flux decreases over the initial time series as the ejecta cool and line blanketing takes effect. We model this unique data set with the non–local thermodynamic equilibrium radiation transport code CMFGEN , finding a good match to the explosion of a low-mass red supergiant with energy E kin = 6 × 10 50 erg. With these models we identify, for the first time, the ions that dominate the early ultraviolet spectra. We present optical photometry and spectroscopy, showing that SN 2022acko has a peak absolute magnitude of V = − 15.4 mag and plateau length of ∼115 days. The spectra closely resemble those of SN 2005cs and SN 2012A. Using the combined optical and ultraviolet spectra, we report the fraction of flux as a function of bluest wavelength on days 5, 7, and 19. We create a spectral time-series of Type II supernovae in the ultraviolet, demonstrating the rapid decline of flux over the first few weeks of evolution. Future observations of Type II supernovae are required to map out the landscape of exploding red supergiants, with and without circumstellar material, which is best revealed in high-quality ultraviolet spectra. 

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2. Physics of Thermonuclear Explosions: Magnetic Field Effects on Deflagration Fronts and Observable Consequences

   https://doi.org/10.3847/1538-4357/ac0ef8  

   Hristov, Boyan; Hoeflich, Peter; Collins, David C. (December 2021, The Astrophysical Journal)

   Abstract We present a study of the influence of magnetic field strength and morphology in Type Ia supernovae and their late-time light curves and spectra. In order to both capture self-consistent magnetic field topologies and evolve our models to late times, a two-stage approach is taken. We study the early deflagration phase (∼1 s) using a variety of magnetic field strengths and find that the topology of the field is set by the burning, independent of the initial strength. We study late-time (∼1000 days) light curves and spectra with a variety of magnetic field topologies and infer magnetic field strengths from observed supernovae. Lower limits are found to be 10 6 G. This is determined by the escape, or lack thereof, of positrons that are tied to the magnetic field. The first stage employs 3D MHD and a local burning approximation and uses the code Enzo. The second stage employs a hybrid approach, with 3D radiation and positron transport and spherical hydrodynamics. The second stage uses the code HYDRA. In our models, magnetic field amplification remains small during the early deflagration phase. Late-time spectra bear the imprint of both magnetic field strength and morphology. Implications for alternative explosion scenarios are discussed. 

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3. Dust masses for a large sample of core-collapse supernovae from optical emission line asymmetries: dust formation on 30-year time-scales

   https://doi.org/10.1093/mnras/stac1626  

   Niculescu-Duvaz, Maria; Barlow, M J; Bevan, A; Wesson, R; Milisavljevic, D; De Looze, I; Clayton, G C; Krafton, K; Matsuura, M; Brady, R (August 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Modelling the red–blue asymmetries seen in the broad emission lines of core-collapse supernovae (CCSNe) is a powerful technique to quantify total dust mass formed in the ejecta at late times (>5 yr after outburst) when ejecta dust temperatures become too low to be detected by mid-infrared (IR) instruments. Following our success in using the Monte Carlo radiative transfer code damocles to measure the dust mass evolution in SN 1987A and other CCSNe, we present the most comprehensive sample of dust mass measurements yet made with damocles, for CCSNe aged between 4 and 60 yr after outburst. Our sample comprises multi-epoch late-time optical spectra taken with the Gemini/Gemini Multi-Object Spectrographs (GMOS) and Very Large Telescope (VLT) X-Shooter spectrographs, supplemented by archival spectra. For the 14 CCSNe that we have modelled, we confirm a dust mass growth with time that can be fit by a sigmoid curve that is found to saturate beyond an age of ∼30 yr, at a mass of 0.23$$^{+0.17}_{-0.12}$$ M⊙. For an expanded sample including dust masses found in the literature for a further 11 CCSNe and six CCSN remnants, the dust mass at saturation is found to be 0.42$$^{+0.09}_{-0.05}$$ M⊙. Uncertainty limits for our dust masses were determined from a Bayesian analysis using the affine invariant Markov chain Monte Carlo ensemble sampler emcee with damocles. The best-fitting line profile models for our sample all required grain radii between 0.1 and 0.5 $$\mu$$m. Our results are consistent with CCSNe forming enough dust in their ejecta to significantly contribute to the dust budget of the Universe. 

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4. Synthetic light curves and spectra from a self-consistent 2D simulation of an ultra-strippped supernova

   https://doi.org/10.1093/mnras/stad3284  

   Maunder, Thomas; Müller, Bernhard; Callan, Fionntan; Sim, Stuart; Heger, Alexander (November 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Spectroscopy is an important tool for providing insights into the structure of core-collapse supernova explosions. We use the Monte Carlo radiative transfer code artis to compute synthetic spectra and light curves based on a two-dimensional explosion model of an ultra-stripped supernova. These calculations are designed both to identify observable fingerprints of ultra-stripped supernovae and as a proof of principle for using synthetic spectroscopy to constrain the nature of stripped-envelope supernovae more broadly. We predict characteristic spectral and photometric features for our ultra-stripped explosion model, and find that these do not match observed ultra-stripped supernova candidates like SN 2005ek. With a peak bolometric luminosity of $$6.8\times 10^{41}\, \mathrm{erg}\, \mathrm{s}^{-1}$$, a peak magnitude of $$-15.9\, \mathrm{mag}$$ in R band, and Δm15,R = 3.50, the model is even fainter and evolves even faster than SN 2005ek as the closest possible analogue in photometric properties. The predicted spectra are extremely unusual. The most prominent features are Mg ii lines at $$2 {,}800\, {\mathring{\rm A}}$$ and $$4 {,}500\, {\mathring{\rm A}}$$ and the infrared Ca triplet at late times. The Mg lines are sensitive to the multidimensional structure of the model and are viewing-angle dependent. They disappear due to line blanketing by iron group elements in a spherically averaged model with additional microscopic mixing. In future studies, multi-D radiative transfer calculations need to be applied to a broader range of models to elucidate the nature of observed Type Ib/c supernovae. 

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5. Type Ia supernovae in the age of JWST: Finding the ‘right’ questions and the path to answers

   https://doi.org/10.1088/1742-6596/2742/1/012024  

   Hoeflich, Peter; Fereidouni, Elham; Mera, Tyco Brahe (April 2024, Journal of Physics: Conference Series)

   Abstract Understanding the Physics of thermonuclear explosions of a White Dwarf star (WD), so called Type Ia Supernovae (SNe Ia), provide a playground for modern physics, computational methods, and are a key to modern cosmology. We identify new and investigate a variety of observational signatures of underlying physical processes related to the thermonuclear runaway, the flame propagation and the environment. Being intrinsically multi-dimensional phenomena, probing the physics requires multi-dimensional radiation-hydrodynamics and MHD simulations. For this task, we developed and employed methods for photon transport for the X-, gamma- and of low energy and of positrons under non-LTE conditions. We identify signatures in the light curves and spectra, in particular, line profiles and polarization spectra. Consistent treatment of high energy processes is critical. Therefore, our framework and results can be used directly a variety of scenarios for SNe Ia including merging WDs and explosions of sub-Chandrasekhar mass WDs. Current simulations have limitations but, nevertheless, when combined with recent JWST and VLT observations solutions emerge to many of decade old problems on the ignition process, flame physics and thermonuclear explosion. 

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