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SN 2021fxy: mid-ultraviolet flux suppression is a common feature of Type Ia supernovae

DerKacy, JM, Paugh, S, Baron, E, Brown, PJ, Ashall, C, Burns, CR, Hsiao, EY, Kumar, S, Lu, J, Morrell, N, Phillips, MM, Shahbandeh, M, Shappee, BJ, Stritzinger, MD, Tucker, MA, Yarbrough, Z, Boutsia, K, Hoeflich, P, Wang, L, Galbany, L , Karamehmetoglu, E, Krisciunas, K, Mazzali, P, Piro, AL, Suntzeff, NB, Fiore, A, Gutiérrez, CP, Lundqvist, P and Reguitti, A (2023) SN 2021fxy: mid-ultraviolet flux suppression is a common feature of Type Ia supernovae. Monthly Notices of the Royal Astronomical Society, 522 (3). pp. 3481-3505. ISSN 0035-8711

SN 2021fxy mid-ultraviolet flux suppression is a common feature of Type Ia supernovae.pdf - Published Version

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We present ultraviolet (UV) to near-infrared (NIR) observations and analysis of the nearby Type Ia supernova SN 2021fxy. Our observations include UV photometry from Swift/UVOT, UV spectroscopy from HST/STIS, and high-cadence optical photometry with the Swope 1-m telescope capturing intranight rises during the early light curve. Early B − V colours show SN 2021fxy is the first 'shallow-silicon' (SS) SN Ia to follow a red-to-blue evolution, compared to other SS objects which show blue colours from the earliest observations. Comparisons to other spectroscopically normal SNe Ia with HST UV spectra reveal SN 2021fxy is one of several SNe Ia with flux suppression in the mid-UV. These SNe also show blueshifted mid-UV spectral features and strong high-velocity Ca II features. One possible origin of this mid-UV suppression is the increased effective opacity in the UV due to increased line blanketing from high velocity material, but differences in the explosion mechanism cannot be ruled out. Among SNe Ia with mid-UV suppression, SNe 2021fxy and 2017erp show substantial similarities in their optical properties despite belonging to different Branch subgroups, and UV flux differences of the same order as those found between SNe 2011fe and 2011by. Differential comparisons to multiple sets of synthetic SN Ia UV spectra reveal this UV flux difference likely originates from a luminosity difference between SNe 2021fxy and 2017erp, and not differing progenitor metallicities as suggested for SNe 2011by and 2011fe. These comparisons illustrate the complicated nature of UV spectral formation, and the need for more UV spectra to determine the physical source of SNe Ia UV diversity.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2023 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press (OUP)
SWORD Depositor: A Symplectic
Date Deposited: 15 Jun 2023 12:53
Last Modified: 15 Jun 2023 13:00
DOI or ID number: 10.1093/mnras/stad1171
URI: https://researchonline.ljmu.ac.uk/id/eprint/19853
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