An Early-time Optical and Ultraviolet Excess in the Type-Ic SN 2020oi

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jats:titleAbstract</jats:title> jats:pWe present photometric and spectroscopic observations of Supernova 2020oi (SN 2020oi), a nearby (∼17 Mpc) type-Ic supernova (SN Ic) within the grand-design spiral M100. We undertake a comprehensive analysis to characterize the evolution of SN 2020oi and constrain its progenitor system. We detect flux in excess of the fireball rise model jats:italicδ</jats:italic> jats:italict</jats:italic> ≈ 2.5 days from the date of explosion in multiband optical and UV photometry from the Las Cumbres Observatory and the Neil Gehrels Swift Observatory, respectively. The derived SN bolometric luminosity is consistent with an explosion with jats:italicM</jats:italic> jats:subej</jats:sub> = 0.81 ± 0.03 jats:italicM</jats:italic> jats:sub⊙</jats:sub>, jats:italicE</jats:italic> jats:sub jats:italick</jats:italic> </jats:sub> = 0.79 ± 0.09 × 10jats:sup51</jats:sup> erg sjats:sup−1</jats:sup>, and jats:italicM</jats:italic> jats:subNi56</jats:sub> = 0.08 ± 0.02 jats:italicM</jats:italic> jats:sub⊙</jats:sub>. Inspection of the event’s decline reveals the highest Δjats:italicm</jats:italic> jats:sub15,bol</jats:sub> reported for a stripped-envelope event to date. Modeling of optical spectra near event peak indicates a partially mixed ejecta comparable in composition to the ejecta observed in SN 1994I, while the earliest spectrum shows signatures of a possible interaction with material of a distinct composition surrounding the SN progenitor. Further, Hubble Space Telescope pre-explosion imaging reveals a stellar cluster coincident with the event. From the cluster photometry, we derive the mass and age of the SN progenitor using stellar evolution models implemented in the jats:monospaceBPASS</jats:monospace> library. Our results indicate that SN 2020oi occurred in a binary system from a progenitor of mass jats:italicM</jats:italic> jats:subZAMS</jats:sub> ≈ 9.5 ± 1.0 jats:italicM</jats:italic> jats:sub⊙</jats:sub>, corresponding to an age of 27 ± 7 Myr. SN 2020oi is the dimmest SN Ic event to date for which an early-time flux excess has been observed, and the first in which an early excess is unlikely to be associated with shock cooling.</jats:p>

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5109 Space Sciences, 51 Physical Sciences, 5101 Astronomical Sciences
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Astrophysical Journal
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American Astronomical Society
European Commission Horizon 2020 (H2020) ERC (101002652)
European Commission Horizon 2020 (H2020) Marie Sk?odowska-Curie actions (873089)