The case for a minute-long merger-driven gamma-ray burst from fast-cooling synchrotron emission
journal contributionposted on 2023-01-20, 11:42 authored by BP Gompertz, ME Ravasio, M Nicholl, AJ Levan, BD Metzger, SR Oates, GP Lamb, WF Fong, DB Malesani, JC Rastinejad, NR Tanvir, PA Evans, PG Jonker, KL Page, A Pe’er
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.
UK Science Technology and Facilities Council grant, ST/S000453/1
B. Gompertz and M. Nicholl are supported by the European ResearchCouncil (ERC) under the European Union’s Horizon 2020 research and innova-tion programme (grant agreement No. 948381, MN). M. Nicholl acknowledgesa Turing Fellowship. A.J. Levan and D.B. Malesani are supported by theEuropean Research Council (ERC) under the European Union’s Horizon 2020research and innovation programme (grant agreement No. 725246, AJL). TheCosmic Dawn Center is funded by the Danish National Research Foundationunder grant No. 140. B.D. Metzger is supported in part by the National ScienceFoundation (grant Nos. Grants AST-2009255, AST-2002577). The FlatironInstitute is supported by the Simons Foundation. G. Lamb is supported by theUK Science Technology and Facilities Council grant, ST/S000453/1. The FongGroup at Northwestern acknowledges support by the National Science Foun-dation under grant Nos. AST-1814782, AST-1909358 and CAREER grant No.AST-2047919. W.F. gratefully acknowledges support by the David and LucilePackard Foundation. P.A. Evans and K.L. Page acknowledge funding from theUK Space Agency.
Author affiliationDepartment of Physics and Astronomy, University of Leicester
- AM (Accepted Manuscript)