A nearby long gamma-ray burst from a merger of compact objects

TL;DR

This paper reports the discovery of a nearby long gamma-ray burst, GRB211211A, which is likely caused by a merger of compact objects, challenging the traditional classification of GRBs by duration.

Contribution

It provides the first conclusive evidence linking a long-duration GRB to a compact binary merger, supported by detailed multi-wavelength observations and kilonova detection.

Findings

GRB211211A is a hybrid event with properties of both long and short GRBs.

The burst is located at a distance of approximately 346 Mpc.

A luminous kilonova was observed, indicating a merger origin.

Abstract

Gamma-ray bursts (GRBs) are flashes of high-energy radiation arising from energetic cosmic explosions. Bursts of long (>2 s) duration are produced by the core-collapse of massive stars, those of short (< 2 s) duration by the merger of two neutron stars (NSs). A third class of events with hybrid high-energy properties was identified, but never conclusively linked to a stellar progenitor. The lack of bright supernovae rules out typical core-collapse explosions, but their distance scales prevent sensitive searches for direct signatures of a progenitor system. Only tentative evidence for a kilonova has been presented. Here we report observations of the exceptionally bright GRB211211A that classify it as a hybrid event and constrain its distance scale to only 346 Mpc. Our measurements indicate that its lower-energy (from ultraviolet to near-infrared) counterpart is powered by a luminous (~1E42 erg/s) kilonova possibly formed in the ejecta of a compact binary merger.