Bright, months-long stellar outbursts announce the explosion of interaction-powered supernovae

TL;DR

This study analyzes pre-explosion outbursts in interaction-powered supernovae, revealing that many exhibit bright, months-long precursors that can eject significant mass, with implications for understanding supernova progenitors and explosion mechanisms.

Contribution

It provides the first systematic detection and characterization of precursor eruptions in a large sample of Type IIn supernovae using forced-photometry light curves from Zwicky Transient Facility data.

Findings

Precursor eruptions detected in 18 Type IIn SNe and one Type Ibn SN.

Precursors become brighter and more frequent in the last months before explosion.

Bright, month-long outbursts occur prior to about 25% of Type IIn SNe within three months of explosion.

Abstract

Interaction-powered supernovae (SNe) explode within an optically-thick circumstellar medium (CSM) that could be ejected during eruptive events. To identify and characterize such pre-explosion outbursts we produce forced-photometry light curves for 196 interacting SNe, mostly of Type IIn, detected by the Zwicky Transient Facility between early 2018 and June 2020. Extensive tests demonstrate that we only expect a few false detections among the 70,000 analyzed pre-explosion images after applying quality cuts and bias corrections. We detect precursor eruptions prior to 18 Type IIn SNe and prior to the Type Ibn SN2019uo. Precursors become brighter and more frequent in the last months before the SN and month-long outbursts brighter than magnitude -13 occur prior to 25% (5 - 69%, 95% confidence range) of all Type IIn SNe within the final three months before the explosion. With radiative energies of up to $10^{49}\,\text{erg}$, precursors could eject $\sim1\,\text{M}_\odot$ of material. Nevertheless, SNe with detected precursors are not significantly more luminous than other SNe IIn and the characteristic narrow hydrogen lines in their spectra typically originate from earlier, undetected mass-loss events. The long precursor durations require ongoing energy injection and they could, for example, be powered by interaction or by a continuum-driven wind. Instabilities during the neon and oxygen burning phases are predicted to launch precursors in the final years to months before the explosion; however, the brightest precursor is 100 times more energetic than anticipated.