Relativistic \(^{56}\text{Ni}\) Decay Lines in GRB 221009A

TL;DR

This paper presents evidence of relativistic nickel decay lines in the prompt emission of GRB 221009A, linking gamma-ray burst emission to supernova nucleosynthesis through Doppler-boosted radioactive decay signatures.

Contribution

It provides the first spectroscopic evidence of relativistic nickel decay lines in a gamma-ray burst, connecting prompt emission features to supernova nucleosynthesis processes.

Findings

Detection of a time-evolving gamma-ray line from 37 to 6 MeV.

Evidence for a higher-energy excess near 24 MeV.

Compatibility of observed flux evolution with radioactive decay models.

Abstract

Long Gamma Ray Bursts are thought to originate from the core collapse of massive stars that give rise to energetic broad-lined Type Ic supernovae. The brightest burst ever recorded, GRB 221009A, has been linked to a broad-lined Type Ic supernova through late-time observations by the James Webb Space Telescope. An emission line evolving from $\sim$37 to $\sim$6~MeV is detected during the prompt phase. We propose that this time-evolving line is consistent with Doppler-boosted radioactive decay of nickel synthesized in the associated supernova and entrained in the relativistic jet, corresponding to the boosted 158~keV decay branch. We also report evidence for an additional higher-energy excess near $\sim$24~MeV at 290--300~s, detected at moderate statistical significance and consistent with the boosted 270~keV decay branch. The observed kinematics and flux evolution are compatible with expectations from radioactive decay, providing direct spectroscopic evidence linking prompt emission to supernova nucleosynthesis.