The case for a minute-long merger-driven gamma-ray burst from fast-cooling synchrotron emission

Benjamin P. Gompertz, Maria Edvige Ravasio, Matt Nicholl, Andrew J. Levan, Brian D. Metzger, Samantha R. Oates, Gavin P. Lamb, Wen-fai Fong, Daniele B. Malesani, Jillian C. Rastinejad, Nial R. Tanvir, Philip A. Evans, Peter G. Jonker, Kim L. Page, Asaf Pe'er

Research output: Contribution to journalArticlepeer-review

42 Citations (Scopus)


For decades, gamma-ray bursts (GRBs) have been broadly divided into long- and short-duration bursts, lasting more or less than 2 s, respectively. However, this dichotomy does not perfectly map to the two progenitor channels that are known to produce GRBs: mergers of compact objects (merger GRBs) or the collapse of massive stars (collapsar GRBs). In particular, the merger GRB population may also include bursts with a short, hard <2 s spike and subsequent longer, softer extended emission. The recent discovery of a kilonova—the radioactive glow of heavy elements made in neutron star mergers—in the 50-s-duration GRB 211211A further demonstrates that mergers can drive long, complex GRBs that mimic the collapsar population. Here we present a detailed temporal and spectral analysis of the high-energy emission of GRB 211211A. We demonstrate that the emission has a purely synchrotron origin, with both the peak and cooling frequencies moving through the γ-ray band down to X-rays, and that the rapidly evolving spectrum drives the extended emission signature at late times. The identification of such spectral evolution in a merger GRB opens avenues to diagnostics of the progenitor type.
Original languageEnglish
Pages (from-to)67-79
Number of pages13
JournalNature Astronomy
Early online date07 Dec 2022
Publication statusPublished - 2023
Externally publishedYes


  • Astrophysics - High Energy Astrophysical Phenomena


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