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 Scopus citations


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
Issue number1
StatePublished - Jan 2023

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© 2022, The Author(s), under exclusive licence to Springer Nature Limited.


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