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

Understand

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 with the Pan-STARRS1 telescope.

• Pre-explosion emission was detected in $riz-$bands at 130 days prior to SN 2020tlf and persisted at relatively constant flux until first light.
• Soon after discovery, &#34;flash&#34; spectroscopy of SN 2020tlf revealed prominent narrow symmetric emission lines ($v_w < 300$ km s$^{-1}$) that resulted from the photo-ionization of unshocked circumstellar material (CSM) shedded in progenitor mass loss episodes in the final weeks to months before explosion.
• Surprisingly, this novel display of pre-SN emission and associated mass loss occurred in a RSG progenitor with ZAMS mass of only 10-12 M$_{\odot}$, as inferred from nebular spectra.