A large fraction of hydrogen-rich supernova progenitors experience elevated mass loss shortly prior to explosion

TL;DR

This study shows that a significant fraction of hydrogen-rich supernova progenitors undergo increased mass loss shortly before explosion, as evidenced by transient emission lines detected in early spectra.

Contribution

It provides the first systematic survey demonstrating that elevated mass loss is common among supernova progenitors using early-time spectroscopic data.

Findings

Over 30% of observed supernovae show transient flash lines indicating mass loss.

At least 60% of early spectra reveal evidence of circumstellar material.

Elevated mass loss shortly before explosion is a widespread phenomenon.

Abstract

Spectroscopic detection of narrow emission lines traces the presence of circumstellar mass distributions around massive stars exploding as core-collapse supernovae. Transient emission lines disappearing shortly after the supernova explosion suggest that the spatial extent of such material is compact, and hence imply an increased mass loss shortly prior to explosion. Here, we present a systematic survey for such transient emission lines (Flash Spectroscopy) among Type II supernovae detected in the first year of the Zwicky Transient Facility (ZTF) survey. We find that at least six out of ten events for which a spectrum was obtained within two days of estimated explosion time show evidence for such transient flash lines. Our measured flash event fraction ($>30\%$ at $95\%$ confidence level) indicates that elevated mass loss is a common process occurring in massive stars that are about to explode as supernovae.