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Arxiv: JWST Spectroscopy of SN H0pe: Classification and Time Delays of a Triply-imaged Type Ia Supernova at z = 1.78 Published: 3/27/2024 11:57:19 PM Updated: 3/27/2024 11:57:19 PM

Paper abstract: SN H0pe is a triply imaged supernova (SN) at redshift z=1.78 discoveredusing the James Webb Space Telescope (JWST). In order to classify the SNspectroscopically and measure the relative time delays of its three images(designated A, B, and C), we acquired NIRSpec follow-up spectroscopy spanning0.6 to 5 microns. From the high signal-to-noise spectra of the two brightimages B and C, we first classify the SN, whose spectra most closely matchthose of SN 1994D and SN 2013dy, as a Type Ia SN. We identify prominentblueshifted absorption features corresponding to Si II \lambda6355 and Ca IIH \lambda3970 and K \lambda3935. We next measure the absolute phases of thethree images from our spectra, which allows us to constrain their relative timedelays. The absolute phases of the three images, determined by fitting thethree spectra to Hsiao07 SN templates, are 6.5_{-1.8}^{+2.4}d,24.3_{-3.9}^{+3.9}d, and 50.6_{-15.3}^{+16.1}d for the brightest tofaintest images. These correspond to relative time delays between Image A andImage B and between Image B and Image C of -122.3_{-43.8}^{+43.7}d and49.3_{-14.7}^{+12.2}d, respectively. The SALT3-NIR model yields phases andtime delays consistent with these values. After unblinding, we additionallyexplored the effect of using Hsiao07 template spectra for simulations througheighty instead of sixty days past maximum, and found a small (11.5 and 1.0days, respectively) yet statistically insignificant (~0.25\sigma and~0.1\sigma) effect on the inferred image delays.