Ultrahigh-energy cosmic-ray signature in GRB 221009A

Saikat Das, Soebur Razzaque

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


The brightest long gamma-ray burst (GRB) detected so far by the Swift-BAT and Fermi-GBM telescopes, GRB 221009A, provides an unprecedented opportunity for understanding the high-energy processes in extreme transient phenomena. We find that the conventional leptonic models for the afterglow emission from this source, synchrotron and synchrotron-self-Compton, have difficulties explaining the observation of ≲10 TeV γ rays (as high as 18 TeV) by the LHAASO detector. We modeled the γ-ray spectrum estimated in the energy range 0.1-1 GeV by the Fermi-LAT detector. The flux predicted by our leptonic models is severely attenuated at > 1 TeV due to γγ pair production with extragalactic background light, and hence an additional component is required at ≲10 TeV. Ultrahigh-energy cosmic rays can be accelerated in the GRB blast wave, and their propagation induces an electromagnetic cascade in the extragalactic medium. The line-of-sight component of this flux can explain the emission at ∼10 TeV detected by LHAASO, which requires a fraction of the GRB blast wave energy to be in ultrahigh-energy cosmic rays. This could be an indication of ultrahigh-energy cosmic-ray acceleration in GRBs.

Original languageEnglish
Article numberL12
JournalAstronomy and Astrophysics
Publication statusPublished - 1 Feb 2023


  • Astroparticle physics
  • Cosmic rays
  • Gamma rays: general
  • Gamma-ray burst: individual: GRB 221009A

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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