A JWST near- and mid-infrared nebular spectrum of the type Ia supernova 2021aefx

Lindsey A. Kwok, Saurabh W. Jha, Tea Temim, Ori D. Fox, Conor Larison, Yssavo Camacho-Neves, Max J. Brenner Newman, Justin D. R. Pierel, Ryan J. Foley, Jennifer E. Andrews, Carles Badenes, Barnabas Barna, K. Azalee Bostroem, Maxime Deckers, Andreas Flors, Peter Garnavich, Melissa L. Graham, Or Graur, Griffin Hosseinzadeh, D. Andrew HowellJohn P. Hughes, Joel Johansson, Sarah Kendrew, Wolfgang E. Kerzendorf, Keiichi Maeda, Kate Maguire, Curtis McCully, John T. O'Brien, Armin Rest, David J. Sand, Melissa Shahbandeh, Louis-Gregory Strolger, Tamas Szalai, Chris Ashall, E. Baron, Chris R. Burns, James M. DerKacy, Tyco Mera Evans, Alec Fisher, Lluis Galbany, Peter Hoeflich, Eric Hsiao, Thomas de Jaeger, Emir Karamehmetoglu, Kevin Krisciunas, Sahana Kumar, Jing Lu, Justyn Maund, Paolo A. Mazzali, Kyle Medler, Nidia Morrell, Mark M. Phillips, Benjamin J. Shappee, Maximilian Stritzinger, Nicholas Suntzeff, Charles Telesco, Michael Tucker, Lifan Wang

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We present JWST near- and mid-infrared spectroscopic observations of the nearby normal Type Ia supernova SN 2021aefx in the nebular phase at +255 days past maximum light. Our Near Infrared Spectrograph (NIRSpec) and Mid Infrared Instrument (MIRI) observations, combined with ground-based optical data from the South African Large Telescope (SALT), constitute the first complete optical + NIR + MIR nebular SN Ia spectrum covering 0.3-14 micron. This spectrum unveils the previously unobserved 2.5-5 micron region, revealing strong nebular iron and stable nickel emission, indicative of high-density burning that can constrain the progenitor mass. The data show a significant improvement in sensitivity and resolution compared to previous Spitzer MIR data. We identify numerous NIR and MIR nebular emission lines from iron-group elements and as well as lines from the intermediate-mass element argon. The argon lines extend to higher velocities than the iron-group elements, suggesting stratified ejecta that are a hallmark of delayed-detonation or double-detonation SN Ia models. We present fits to simple geometric line profiles to features beyond 1.2 micron and find that most lines are consistent with Gaussian or spherical emission distributions, while the [Ar III] 8.99 micron line has a distinctively flat-topped profile indicating a thick spherical shell of emission. Using our line profile fits, we investigate the emissivity structure of SN 2021aefx and measure kinematic properties. Continued observations of SN 2021aefx and other SNe Ia with JWST will be transformative to the study of SN Ia composition, ionization structure, density, and temperature, and will provide important constraints on SN Ia progenitor and explosion models.
Original languageEnglish
Article numberL3
Number of pages15
JournalAstrophysical Journal Letters
Publication statusPublished - 8 Feb 2023


  • astro-ph.HE
  • astro-ph.SR


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