SN 2016coi (ASASSN-16fp): An Energetic H-stripped Core-collapse Supernova from a Massive Stellar Progenitor with Large Mass Loss

Abstract

We present comprehensive observations and analysis of the energetic H-stripped SN 2016coi (a.k.a. ASASSN-16fp), spanning the γ-ray through optical and radio wavelengths, acquired within the first hours to ∼420 days post explosion. Our observational campaign confirms the identification of He in the SN ejecta, which we interpret to be caused by a larger mixing of Ni into the outer ejecta layers. From the modeling of the broad bolometric light curve we derive a large ejecta mass to kinetic energy ratio (M ej ∼ 4 − 7 M , E k ∼ 7 − 8 × 10 51 erg). The small [Ca II] λλ7291,7324 to [O I] λλ6300,6364 ratio (∼0.2) observed in our latetime optical spectra is suggestive of a large progenitor core mass at the time of collapse. We find that SN 2016coi is a luminous source of X-rays (L X > 10 39 erg s −1 in the first ∼ 100 days post explosion) and radio emission (L 8.5 GHz ∼ 7 × 10 27 erg s −1 Hz −1 at peak). These values are in line with those of relativistic SNe (2 pre-explosion progenitor mass-loss with rateṀ ∼ (1 − 2) × 10 −4 M yr −1 and a sub-relativistic shock velocity v sh ∼ 0.15c, in stark contrast with relativistic SNe and similar to normal SNe. Finally, we find no evidence for a SN-associated shock breakout γ-ray pulse with energy E γ > 2 × 10 46 erg. While we cannot exclude the presence of a companion in a binary system, taken together, our findings are consistent with a massive single star progenitor that experienced large mass loss in the years leading up to core-collapse, but was unable to achieve complete stripping of its outer layers before explosion.

Radio Emission from Ultra-stripped Supernovae as Diagnostics for Properties of the Remnant Double Neutron Star Binaries

“…In the model sep 10Rsun, the peak date of the radio luminosity at 8.46 GHz is at 10 -100 days, which is similar to the observed radio peak dates for typical Type Ib/Ic SNe (see e.g., Margutti et al 2014;Terreran et al 2019). However, the maximum luminosity is smaller than those of the typical Type Ib/Ic SNe, because of the low explosion energy of the ultra-stripped SNe (see also Section 5.3).…”

Constraints on the Sub-pc Environment of the Nearby Type Iax SN 2014dt from Deep X-ray and Radio Observations

“…We compare these limits to those for 𝜖 B = 0.01 of SNe Iax 2012Z (Chomiuk et al 2015) and 2019muj (derived in Appendix A using the radio upper limits from Perez-Torres et al 2019), and SNe Ia 2014J (Chomiuk et al 2014), 2011fe (Chomiuk et al 2012), and the type Ia-CSM PTF11kx (Dilday et al 2012;Chomiuk et al 2015) where 𝜖 B = 0.01. Using the observed mass-loss rates and wind velocities in massive stars from Chomiuk et al (2012) and Terreran et al (2019), we find that a portion of the parameter space associated with giant star (GS) companions and Wolf-Rayet (WR) stars is ruled out for 𝜖 b = 0.1 for SN 2014dt. For both values of 𝜖 𝐵 we can rule out Red Super Giant Stars (RSG) and most of the Luminous Blue Variable (LBV) stars wind-like CSM parameter space.…”

The final months of massive star evolution from the circumstellar environment around SN Ic 2020oi

“…The situation is similar for broadlined SNe Ic, for which radio follow-up observation is routinely undertaken (e.g., Corsi et al 2016). They tend to show the CSM density at 10 16 cm being lower than for typical SESNe except for a few cases (Terreran et al 2019;Nayana & Chandra 2020), while little is known about the nature of CSM at the scale of ∼ 10 15 cm. While very rapid radio follow-up observations have been conducted for a few broadlined SNe Ic associated with a long Gamma-Ray Burst (GRB), the physical scale of the CSM probed at a few days after the explosion is already at ∼ > a few ×10 15 cm for these GRB-SNe due to the (sub) relativistic ejecta creating the synchrotron emission (Kulkarni et al 1998).…”