Signatures of an eruptive phase before the explosion of the peculiar core-collapse SN 2013gc

Abstract

We present photometric and spectroscopic analysis of the peculiar core-collapse SN 2013gc, spanning seven years of observations. The light curve shows an early maximum followed by a fast decline and a phase of almost constant luminosity. At +200 days from maximum, a brightening of 1 mag is observed in all bands, followed by a steep linear luminosity decline after +300 d. In archival images taken between 1.5 and 2.5 years before the explosion, a weak source is visible at the supernova location, with mag≈20. The early supernova spectra show Balmer lines, with a narrow (∼560 km s −1 ) P-Cygni absorption superimposed on a broad (∼3400 km s −1 ) component, typical of type IIn events. Through a comparison of colour curves, absolute light curves and spectra of SN 2013gc with a sample of supernovae IIn, we conclude that SN 2013gc is a member of the so-called type IId subgroup. The complex profile of the Hα line suggests a composite circumstellar medium geometry, with a combination of lower velocity, spherically symmetric gas and a more rapidly expanding bilobed feature. This circumstellar medium distribution has been likely formed through major massloss events, that we directly observed from 3 years before the explosio. The modest luminosity (M I ∼ −16.5 near maximum) of SN 2013gc at all phases, the very small amount of ejected 56 Ni (of the order of 10 −3 M ), the major pre-supernova stellar activity and the lack of prominent [O i] lines in late-time spectra support a fall-back core-collapse scenario for the massive progenitor of SN 2013gc.

SN 2017gmr: An Energetic Type II-P Supernova with Asymmetries

“…With the advent of high-cadence transient searches in the past decade, several instances of pre-SN outbursts have been observed directly in the months to years before explosion (e.g., Fraser et al 2013;Mauerhan et al 2013;Ofek et al 2013Ofek et al , 2014Elias-Rosa et al 2016;Tartaglia et al 2016;Reguitti et al 2019), although overall detectable outbursts are rare (Bilinski et al 2015;Strotjohann et al 2015). These outbursts are generally associated with SNe that have substantial circumstellar material as evidenced by their SN IIn-like behavior.…”

Bright, Months-long Stellar Outbursts Announce the Explosion of Interaction-powered Supernovae

“…The first pre-explosion outburst was detected two years prior to the explosion of the Type Ibn SN 2006jc (Pastorello et al 2007;Foley et al 2007). Most precursors were observed prior to Type IIn SNe (see, e.g., Fraser et al 2013;Mauerhan et al 2013;Margutti et al 2013;Ofek et al 2013b;Elias-Rosa et al 2016;Tartaglia et al 2016;Ofek et al 2016;Thöne et al 2017;Nyholm et al 2017;Pastorello et al 2018;Reguitti et al 2019), as well as prior to a broad-lined Type Ic SN (Ho et al 2019) and possibly an SN IIb (Strotjohann et al 2015). This suggests that numerous types of progenitor stars can produce such flares.…”

A systematic reclassification of Type IIn supernovae

“…6), where there may be a double-peaked H profile, and at later epochs a "hump" appears on the red side of the profile. A further example of this profile diversity is the proposed subclass SN IId (Benetti 2000); examples of SNe IId within our catalogue may include SN 2009kn and SN 2013gc (Reguitti et al 2019). There are 4000 4500 5000 5500 6000 6500 7000 7500 8000…”

“…SNe IIn typically have spectra that exhibit enduring CSM interaction. Some subcategories are also used such as SN IIn-P and IIn-L, but also SN IId where the narrow H line has a P Cygni profile, such as in SN 2013gc (Benetti 2000;Reguitti et al 2019). Furthermore, at later epochs an object may be reclassified (for example, as a standard SN II) and online resources mark the object with the new classification despite the previous evidence of CSM interaction.…”