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

Abstract

We 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 δ t ≈ 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 M ej = 0.81 ± 0.03 M ⊙, E k = 0.79 ± 0.09 × 1051 erg s−1, and M Ni56 = 0.08 ± 0.02 M ⊙. Inspection of the event’s decline reveals the highest Δm 15,bol 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 BPASS library. Our results indicate that SN 2020oi occurred in a binary system from a progenitor of mass M ZAMS ≈ 9.5 ± 1.0 M ⊙, 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.

SN 2022oqm -- a Ca-rich explosion of a compact progenitor embedded in C/O circumstellar material

“…SN 2022oqm shows several peculiarities separating it from the general SN Ic population. It has an early peak only seen in several other SNe Ic-BL and SNe Ic, a C/O CSM, directly observed so far only in rare cases such as SNe Icn (e.g., Ben-Ami et al 2014;Gal-Yam et al 2022;Perley et al 2022;Gagliano et al 2022;Pellegrino et al 2022), and indirectly implied for SN 2018gep through its precursor emission (Ho et al 2019). Its Ca-rich nebular spectrum, peak luminosity at 12 days and offset loca-tion are consistent with the Ca-rich population (Perets et al 2010;Kasliwal et al 2012;De et al 2018).…”

“…Occasionally, a coincident gammaray burst (GRB) or X-ray flash (XRF) resulted in intense UV-optical follow-up observations (Campana et al 2006;Soderberg et al 2008). Several other well-studied normal and peculiar SNe Ic (De et al 2018;Horesh et al 2020), broad-lined SNe Ic (Ic-BL; reported by Ho et al 2019Ho et al , 2020a, and SNe Icn (Gal-Yam et al 2022;Perley et al 2022;Pellegrino et al 2022;Gagliano et al 2022) have been found, showing diverse properties. In some of these cases, a short-lived early blue peak has been observed, possibly consistent with the shock cooling of a low-mass envelope, shock-breakout from a confined shell of CSM, or the subsequent cooling of the shocked material.…”

Evidence for Extended Hydrogen-Poor CSM in the Three-Peaked Light Curve of Stripped Envelope Ib Supernova

“…In the context of SN Ia correlation between the observed luminosity at the maximum light to the 56 Ni see (Stritzinger et al 2006). (Arnett 1982;Stritzinger et al 2006;Gagliano et al 2022). 𝛾-rays released in this process are then thermalized in the expanding SN ejecta and, for phases 𝑡 60 days after explosion, 56 Co beta-decay will power the bolometric light curve until the decays of other radioactive species such as 57 Co and 55 Fe become dominant (e.g., 𝑡 50 days after explosion; red dot-dashed line in Fig.…”

“…where 𝑡 Ni = 8.77 days, 𝑡 Co = 111.3 days is the timescale for the radioactive decay of 56 Ni into 56 Co and 56 Co into 56 Fe, and 𝜀 Ni = 3.9×10 10 erg g −1 s −1 and 𝜀 Co = 6.8×10 9 erg g −1 s −1 are the specific heating rates (the amount of energy per unit mass released) from these decays (in solar mass units: 𝜀 Ni = 6.45 × 10 43 erg s −1 M −1 and 𝜀 Co = 1.45 × 10 43 erg s −1 M −1 ). We adopt a value of 𝛽 = 0.9, suitable for SNe Ic (Gagliano et al 2022). The diffusion timescale 𝑡 𝑑 can be calculated from the rise time 𝑡 𝑠 by numerically solving the equation…”

“…In Figure 4, we compare the SN 2019tsf light curve to some prototypical SNe Ib and Ic such as SN 2019yvr, SN 2017ein, SN 2020oi respectively, and we conclude that the SN 2019tsf light curve behaves like a SN Ib. Nevertheless, we estimate the 56 Ni mass by following (Dessart et al 2011(Dessart et al , 2015Khatami & Kasen 2019;Gagliano et al 2022) and find that it could be powered by 0.07 − 0.12 M (see fig. 11).…”