A JWST Near- and Mid-Infrared Nebular Spectrum of the Type Ia Supernova 2021aefx

Serendipitous Nebular-phase JWST Imaging of SN Ia SN 2021aefx: Testing the Confinement of 56Co Decay Energy

“…Table 1 also reports νL ν and ΔνL ν , calculated by converting the flux density to a luminosity (L ν ) and then multiplying by the frequency at the nominal filter center, 35,36 ν, and the nominal frequency width of the filter, Δν, respectively. ΔνL ν is a more useful physical measurement than νL ν because it more nearly corresponds to a direct integral over the filter, 37 and the emission from the SN is expected to be localized line emission (e.g., Fransson & Jerkstrand 2015;Kwok et al 2022).…”

“…We compute synthetic photometry from the 0.3-14 μm +255-day spectrum of SN 2021aefx published by Kwok et al (2022), so we briefly discuss the precision of the spectral flux calibration. JWST is currently obtaining Cycle 1 calibration observations, so the absolute flux calibration has not been finalized.…”

“…Johansson et al 2017 analyzed multiepoch Spitzer light curves of SNe Ia extending into the nebular phase but were limited to the CH1 (3.6 μm) and CH2 (4.5 μm) bandpasses. Kwok et al (2022) and DerKacy et al (2023) recently published spectra of SN 2021aefx extending to 14 μm with JWST at +255 and +323 days after maximum light, respectively. SN 2014J has multiple mid-IR spectra (Telesco et al 2015), with the caveat that the spectra were obtained from the ground with the Gran Telescopio Canarias, where the high sky brightness and low atmospheric transmission in the mid-IR complicate precise flux calibration.…”

“…The brightness and close proximity of SN 2021aefx make it an excellent target for nebular-phase JWST observations. Kwok et al (2022) andDerKacy et al (2023) provided the first demonstration of the impressive spectroscopic capabilities of JWST for studying nebular-phase SNe Ia. Their spectra of SN 2021aefx, obtained +255 and +323 days after t max , respectively, represent the highest-quality look at the emission properties >2.5 μm of SNe Ia to date.…”

“…Our new 2-21 μm JWST photometry at +357 days is used in conjunction with the +255-day 0.3-14 μm spectrum from Kwok et al (2022) to (1) provide the time-dependent fraction of flux emerging at optical, near-IR, and mid-IR wavelengths and (2) determine whether the decline rate of the 0.3-14 μm flux is consistent with expectations for the radioactive decay of 56 Co → 56 Fe. The imaging data and reduction are described in Section 2.…”