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1. Numerical Simulations of Convective Three-dimensional Red Supergiant Envelopes

   https://doi.org/10.3847/1538-4357/ac5ab3  

   Goldberg, Jared A. ; Jiang 姜, Yan-Fei 燕飞 ; Bildsten, Lars ( April 2022 , The Astrophysical Journal)

   We explore the three-dimensional properties of convective, luminous (L≈ 10^4.5–10⁵L_⊙), hydrogen-rich envelopes of red supergiants (RSGs) based on radiation hydrodynamic simulations in spherical geometry usingAthena++. These computations comprise ≈30% of the stellar volume, include gas and radiation pressure, and self-consistently track the gravitational potential for the outer ≈3M_⊙of the simulatedM≈ 15M_⊙stars. This work reveals a radius,R_corr, around which the nature of the convection changes. Forr>R_corr, though still optically thick, diffusion of photons dominates the energy transport. Such a regime is well studied in less luminous stars, but in RSGs, the near- (or above-)Eddington luminosity (due to opacity enhancements at ionization transitions) leads to the unusual outcome of denser regions moving outward rather than inward. This region of the star also has a large amount of turbulent pressure, yielding a density structure much more extended than 1D stellar evolution predicts. This “halo” of material will impact predictions for both shock breakout and early lightcurves of Type IIP supernovae. Inside ofR_corr, we find a nearly flat entropy profile as expected in the efficient regime of mixing-length theory (MLT). Radiation pressure provides ≈1/3 of the support against gravity in this region. Our comparisons to MLT suggest a mixing length ofα= 3–4, consistent with the sizes of convective plumes seen in the simulations. The temporal variability of these 3D models is mostly on the timescale of the convective plume lifetimes (≈300 days), with amplitudes consistent with those observed photometrically.

    

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2. Black hole to breakout: 3D GRMHD simulations of collapsar jets reveal a wide range of transients

   https://doi.org/10.1093/mnras/stab3784  

   Gottlieb, Ore ; Lalakos, Aretaios ; Bromberg, Omer ; Liska, Matthew ; Tchekhovskoy, Alexander ( January 2022 , Monthly Notices of the Royal Astronomical Society)

   We present a suite of the first 3D GRMHD collapsar simulations, which extend from the self-consistent jet launching by an accreting Kerr black hole (BH) to the breakout from the star. We identify three types of outflows, depending on the angular momentum, l, of the collapsing material and the magnetic field, B, on the BH horizon: (i) subrelativistic outflow (low l and high B), (ii) stationary accretion shock instability (SASI; high l and low B), (iii) relativistic jets (high l and high B). In the absence of jets, free-fall of the stellar envelope provides a good estimate for the BH accretion rate. Jets can substantially suppress the accretion rate, and their duration can be limited by the magnetization profile in the star. We find that progenitors with large (steep) inner density power-law indices (≳ 2), face extreme challenges as gamma-ray burst (GRB) progenitors due to excessive luminosity, global time evolution in the light curve throughout the burst and short breakout times, inconsistent with observations. Our results suggest that the wide variety of observed explosion appearances (supernova/supernova + GRB/low-luminosity GRBs) and the characteristics of the emitting relativistic outflows (luminosity and duration) can be naturally explained by the differences in the progenitor structure. Our simulations reveal several important jet features: (i) strong magnetic dissipation inside the star, resulting in weakly magnetized jets by breakout that may have significant photospheric emission and (ii) spontaneous emergence of tilted accretion disc-jet flows, even in the absence of any tilt in the progenitor.

    

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3. SN 2023ixf in Messier 101: Photo-ionization of Dense, Close-in Circumstellar Material in a Nearby Type II Supernova

   https://doi.org/10.3847/2041-8213/acf2ec  

   Jacobson-Galán, W. V. ; Dessart, L. ; Margutti, R. ; Chornock, R. ; Foley, R. J. ; Kilpatrick, C. D. ; Jones, D. O. ; Taggart, K. ; Angus, C. R. ; Bhattacharjee, S. ; et al ( September 2023 , The Astrophysical Journal Letters)

   We present UV and/or optical observations and models of SN 2023ixf, a type II supernova (SN) located in Messier 101 at 6.9 Mpc. Early time (flash) spectroscopy of SN 2023ixf, obtained primarily at Lick Observatory, reveals emission lines of Hi, Hei/ii, Civ, and Niii/iv/vwith a narrow core and broad, symmetric wings arising from the photoionization of dense, close-in circumstellar material (CSM) located around the progenitor star prior to shock breakout. These electron-scattering broadened line profiles persist for ∼8 days with respect to first light, at which time Doppler broadened the features from the fastest SN ejecta form, suggesting a reduction in CSM density atr≳ 10¹⁵cm. The early time light curve of SN 2023ixf shows peak absolute magnitudes (e.g.,M_u= −18.6 mag,M_g= −18.4 mag) that are ≳2 mag brighter than typical type II SNe, this photometric boost also being consistent with the shock power supplied from CSM interaction. Comparison of SN 2023ixf to a grid of light-curve and multiepoch spectral models from the non-LTE radiative transfer codeCMFGENand the radiation-hydrodynamics codeHERACLESsuggests dense, solar-metallicity CSM confined tor= (0.5–1) × 10¹⁵cm, and a progenitor mass-loss rate of$\dot{M}={10}^{-2}{M}_{\odot }$yr⁻¹. For the assumed progenitor wind velocity ofv_w= 50 km s⁻¹, this corresponds to enhanced mass loss (i.e.,superwindphase) during the last ∼3–6 yr before explosion.

    

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4. Supernova Precursor Emission and the Origin of Pre-explosion Stellar Mass Loss

   https://doi.org/10.3847/1538-4357/ac892c  

   Matsumoto, Tatsuya ; Metzger, Brian D. ( September 2022 , The Astrophysical Journal)

   A growing number of core-collapse supernovae (SNe) that show evidence for interaction with dense circumstellar medium (CSM) are accompanied by “precursor” optical emission rising weeks to months prior to the explosion. The precursor luminosities greatly exceed the Eddington limit of the progenitor star, implying that they are accompanied by substantial mass loss. Here, we present a semi-analytic model for SN precursor light curves, which we apply to constrain the properties and mechanisms of the pre-explosion mass loss. We explore two limiting mass-loss scenarios: (1) an “eruption” arising from shock breakout following impulsive energy deposition below the stellar surface; and (2) a steady “wind,” due to sustained heating of the progenitor envelope. The eruption model, which resembles a scaled-down version of Type IIP SNe, can explain the luminosities and timescales of well-sampled precursors, for ejecta masses ∼ 0.1–1M_⊙and velocities ∼ 100–1000 km s⁻¹. By contrast, the steady wind scenario cannot explain the highest precursor luminosities ≳ 10⁴¹erg s⁻¹, under the constraint that the total ejecta mass does not exceed the entire progenitor mass (though the less luminous SN 2020tlf precursor can be explained by a mass-loss rate ∼ 1M_⊙yr⁻¹). However, shock interaction between the wind and pre-existing (earlier ejected) CSM may boost its radiative efficiency and mitigate this constraint. In both the eruption and wind scenarios, the precursor ejecta forms compact (≲10¹⁵cm) optically thick CSM at the time of core collapse; though only directly observable via rapid post-explosion spectroscopy (≲ a few days before being overtaken by the SN ejecta), this material can boost the SN luminosity via shock interaction.

    

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5. Final Moments. I. Precursor Emission, Envelope Inflation, and Enhanced Mass Loss Preceding the Luminous Type II Supernova 2020tlf

   https://doi.org/10.3847/1538-4357/ac3f3a  

   Jacobson-Galán, W. V. ; Dessart, L. ; Jones, D. O. ; Margutti, R. ; Coppejans, D. L. ; Dimitriadis, G. ; Foley, R. J. ; Kilpatrick, C. D. ; Matthews, D. J. ; Rest, S. ; et al ( January 2022 , The Astrophysical Journal)

   Abstract We present panchromatic observations and modeling of supernova (SN) 2020tlf, the first normal Type II-P/L SN with confirmed precursor emission, as detected by the Young Supernova Experiment transient survey. Pre-SN activity was detected in riz -bands at −130 days and persisted at relatively constant flux until first light. Soon after discovery, “flash” spectroscopy of SN 2020tlf revealed narrow, symmetric emission lines that resulted from the photoionization of circumstellar material (CSM) shed in progenitor mass-loss episodes before explosion. Surprisingly, this novel display of pre-SN emission and associated mass loss occurred in a red supergiant (RSG) progenitor with zero-age main-sequence mass of only 10–12 M ⊙ , as inferred from nebular spectra. Modeling of the light curve and multi-epoch spectra with the non-LTE radiative-transfer code CMFGEN and radiation-hydrodynamical code HERACLES suggests a dense CSM limited to r ≈ 10 15 cm, and mass-loss rate of 10 −2 M ⊙ yr −1 . The luminous light-curve plateau and persistent blue excess indicates an extended progenitor, compatible with an RSG model with R ⋆ = 1100 R ⊙ . Limits on the shock-powered X-ray and radio luminosity are consistent with model conclusions and suggest a CSM density of ρ < 2 × 10 −16 g cm −3 for distances from the progenitor star of r ≈ 5 × 10 15 cm, as well as a mass-loss rate of M ̇ < 1.3 × 10 − 5 M ☉ yr − 1 at larger distances. A promising power source for the observed precursor emission is the ejection of stellar material following energy disposition into the stellar envelope as a result of gravity waves emitted during either neon/oxygen burning or a nuclear flash from silicon combustion. 

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