Final Moments. I. Precursor Emission, Envelope Inflation, and Enhanced Mass Loss Preceding the Luminous Type II Supernova 2020tlf

Abstract

We present panchromatic observations and modeling of supernova (SN) 2020tlf, the first normal Type II-P/L SN with confirmed precursor emission, as detected by the Young Supernova Experiment transient survey. Pre-SN activity was detected in riz-bands at −130 days and persisted at relatively constant flux until first light. Soon after discovery, “flash” spectroscopy of SN 2020tlf revealed narrow, symmetric emission lines that resulted from the photoionization of circumstellar material (CSM) shed in progenitor mass-loss episodes before explosion. Surprisingly, this novel display of pre-SN emission and associated mass loss occurred in a red supergiant (RSG) progenitor with zero-age main-sequence mass of only 10–12 M ⊙, as inferred from nebular spectra. Modeling of the light curve and multi-epoch spectra with the non-LTE radiative-transfer code CMFGEN and radiation-hydrodynamical code HERACLES suggests a dense CSM limited to r ≈ 1015 cm, and mass-loss rate of 10−2 M ⊙ yr−1. The luminous light-curve plateau and persistent blue excess indicates an extended progenitor, compatible with an RSG model with R ⋆ = 1100 R ⊙. Limits on the shock-powered X-ray and radio luminosity are consistent with model conclusions and suggest a CSM density of ρ < 2 × 10−16 g cm−3 for distances from the progenitor star of r ≈ 5 × 1015 cm, as well as a mass-loss rate of M ̇ < 1.3 × 10 − 5 M ☉ yr − 1 at larger distances. A promising power source for the observed precursor emission is the ejection of stellar material following energy disposition into the stellar envelope as a result of gravity waves emitted during either neon/oxygen burning or a nuclear flash from silicon combustion.

Circumstellar shell and presupernova emission of SN 2020tlf

“…In this row is the type II SN 2020tlf that should be classified as IIP, since the light curve has a plateau with a clear-cut transition to the radioactive tail. Apart from a confined dense shell, this supernova is remarkable for the preSN emission during 130 days before the explosion with the super-Eddington luminosity of ≈10 40 erg s −1 that presumably is associated with the formation of the CS shell (Jacobson-Galán et al 2022). Authors conclude that it is the matter lost at the stage of preSN high luminosity that is observed on day 10 in CS emission lines.…”

High energy particles from young supernovae: gamma-ray and neutrino connections

“…The typical mass loss rate during this phase has been reported to be O(10 −3 ) Ṁ yr −1 [130][131][132]. Larger mass loss rates [O(1) Ṁ yr −1 ] have also been predicted, see [124,125]; however, these do not seem to be consistent with other studies of II-P SNe (see e.g., [71,133,134]) 4 . Therefore, we adopt 10 −2 Ṁ yr −1 as our typical mass loss rate.…”

“…• Type II-L SNe have linear light curves, while Type II-b show broad hydrogen lines in their spectra. Their progenitors have similar mass loss rates, which lie in the range 10 −5 -10 −4 Ṁ yr −1 and have wind velocity between 2 × 10 1 -10 2 km s −1 [63,71,[135][136][137][138][139]. The shock velocity for these Types of SNe is found to be of the order of 10 4 km/s [140].…”

“…This is due to the photo-ionization of the CSM occurring during the progenitor mass loss phase before explosion, see e.g. [71,72]. UV/optical excesses observed in SNe at early times also hint towards such mass loss phenomena, see e.g.…”

Modeling the signatures of interaction in Type II supernovae: UV emission, high-velocity features, broad-boxy profiles

“…While the existence of CSM is not surprising for massive stars, a number of observed SNe suggest that this CSM may be exceptionally dense, in the sense that it would correspond to wind mass loss rates manyfold greater than standard steady-state mass loss rates typically in-ferred in massive stars (see, for example, de Jager et al 1988). This CSM may also extend out to large distances above the star surface, from several 10 14 cm (SN 2013fs; Dessart et al 2017;Moriya et al 2017;Morozova et al 2017;Yaron et al 2017), to 10 15 cm (SN 2020tlf;Jacobson-Galán et al 2022), to several 10 15 cm (SN 1998S; Leonard et al 2000;Fassia et al 2001;Chugai 2001;Dessart et al 2016), and up to 10 16 cm (SN 2010jl; Zhang et al 2012;Fransson et al 2014;Dessart et al 2015). While large relative to the progenitor radius, these distances correspond to mass loss episodes occurring on year time scales before core collapse and thus may point to dynamical phenomena tied to the last stages of massive star evolution (Quataert & Shiode 2012;Fuller 2017).…”