TeV afterglow from GRB 221009A: photohadronic origin?

TL;DR

This paper reports the first observation of multi-TeV gamma-ray spectra during the afterglow of GRB 221009A, explained by a photohadronic model involving high-energy protons interacting with SSC photons.

Contribution

It introduces a novel photohadronic explanation for the TeV afterglow spectra of GRB 221009A, linking it to similar spectra observed in EHBLs.

Findings

Detection of multi-TeV photons up to 13 TeV during GRB afterglow

Spectral analysis consistent with photohadronic model including EBL effects

First observation of such spectra in a GRB context

Abstract

Gamma-ray burst (GRB), GRB 221009A, a long-duration GRB, was observed simultaneously by the Water Cherenkov Detector Array (WCDA) and the Kilometer Squared Array (KM2A) of the Large High Altitude Air Shower Observatory (LHAASO) during the prompt emission and the afterglow periods. Characteristic multi-TeV photons up to 13 TeV were observed in the afterglow phase. The observed very high-energy (VHE) gamma-ray spectra by WCDA and KM2A during different time intervals and in different energy ranges can be explained very well in the context of the photohadronic model with the inclusion of extragalactic background light models. In the photohadronic scenario, interaction of high-energy protons with the synchrotron self-Compton (SSC) photons in the forward shock region of the jet is assumed to be the source of these VHE photons. The observed VHE spectra from the afterglow of GRB 221009A are similar to the VHE gamma-ray spectra observed from the temporary extreme high-energy peaked BL Lac (EHBL), 1ES 2344+514 {\it only} during the 11th and the 12th of August, 2016. Such spectra are new and have been observed for the first time in a GRB.