Circumstellar Material Ejected Violently by A Massive Star Immediately before its Death

TL;DR

This study analyzes the circumstellar material ejected by the progenitor of supernova SN 2023ixf shortly before its explosion, revealing a high mass-loss rate and a dense shell close to the star, providing insights into the final stages of massive star evolution.

Contribution

First detailed constraints on the circumstellar environment of SN 2023ixf using early spectra, indicating recent intense mass loss from the progenitor.

Findings

Progenitor lost material at ~6 x 10^{-4} M_sun/year in last 2-3 years.

Circumstellar shell located within 7 x 10^{14} cm of the star.

Progenitor likely a yellow hypergiant evolving from a red supergiant.

Abstract

Type II supernovae represent the most common stellar explosions in the Universe, for which the final stage evolution of their hydrogen-rich massive progenitors towards core-collapse explosion are elusive. The recent explosion of SN 2023ixf in a very nearby galaxy, Messier 101, provides a rare opportunity to explore this longstanding issue. With the timely high-cadence flash spectra taken within 1-5 days after the explosion, we can put stringent constraints on the properties of the surrounding circumstellar material around this supernova. Based on the rapid fading of the narrow emission lines and luminosity/profile of $\rm H\alpha$ emission at very early times, we estimate that the progenitor of SN 2023ixf lost material at a mass-loss rate $\dot{\rm M} \approx 6 \times 10^{-4}\, \rm M_{\odot}\,a^{-1}$ over the last 2-3 years before explosion. This close-by material, moving at a velocity $v_{\rm w} \approx 55\rm \, km\,s^{-1}$, accumulates a compact CSM shell at the radius smaller than $7 \times 10^{14}$ cm from the progenitor. Given the high mass-loss rate and relatively large wind velocity presented here, together with the pre-explosion observations made about two decades ago, the progenitor of SN 2023ixf could be a short-lived yellow hypergiant that evolved from a red supergiant shortly before the explosion.