Fermi-LAT Detection of a GeV Afterglow from a Compact Stellar Merger

Abstract

It is usually thought that long-duration gamma-ray bursts (GRBs) are associated with massive star core collapse, whereas short-duration GRBs are associated with mergers of compact stellar binaries. The discovery of a kilonova associated with a nearby (350 Mpc) long-duration GRB-GRB 211211A, however, indicates that the progenitor of this long-duration GRB is a compact object merger. Here we report the Fermi-LAT detection of gamma-ray ($>100\mathrm{MeV}$) afterglow emission from GRB 211211A, which lasts $\sim$20,000 s after the burst, the longest event for conventional short-duration GRBs ever detected. We suggest that this gamma-ray emission results from afterglow synchrotron emission. The soft spectrum of GeV emission may arise from a limited maximum synchrotron energy of only a few hundreds of MeV at $\sim$20,000 s. The unusually long duration of the GeV emission could be due to the proximity of this GRB and the long deceleration time of the GRB jet that is expanding in a low-density circumburst medium, consistent with the compact stellar merger scenario.

Correction of a typo

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• GRB 211211A: a Neutron Star$-$White Dwarf Merger?
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• GRB 211211A-like Events and How Gravitational Waves May Tell Their Origins
• Evidence for a compact stellar merger origin for GRB 230307A from Fermi-LAT and multi-wavelength afterglow observations
• High-energy neutrino emission associated with gravitational-wave signals: effects of cocoon photons and constraints on late-time emission
• Shared Properties of Merger-driven Long-duration Gamma-Ray Bursts
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• Searching for gravitational waves from compact binary mergers powering long gamma-ray bursts during LIGO-Virgo-KAGRA's O3 run