Carpet-3 detection of a photon-like air shower with estimated primary energy above 100 TeV in a spatial and temporal coincidence with GRB 221009A

TL;DR

This paper reports the detection of a 300 TeV photon-like air shower coincident with GRB 221009A, using the Carpet-3 detector and machine learning, providing insights into high-energy photon propagation and astrophysical models.

Contribution

The study presents the highest-energy photon event associated with a GRB, utilizing upgraded detector technology and advanced analysis methods to improve detection and characterization.

Findings

Detected a 300 TeV photon-like air shower coincident with GRB 221009A.

Estimated the primary energy with uncertainties of +43/-38 TeV.

Determined the probability of the event being hadronic as approximately 3 x 10^{-4}.

Abstract

The brightest cosmic gamma-ray burst (GRB) ever detected, GRB 221009A, was accompanied by photons of very high energies. These gamma rays may be used to test both the astrophysical models of the burst and our understanding of long-distance propagation of energetic photons, including potential new-physics effects. Here we present the observation of a photon-like air shower with the estimated primary energy of $300^{+43}_{-38}$ TeV, coincident (with the chance probability of $\sim 9\cdot 10^{-3}$) with the GRB in its arrival direction and time. Making use of the upgraded Carpet-3 muon detector and new machine learning analysis, we estimate the probability that the primary was hadronic as $\sim 3 \cdot 10^{-4}$. This is the highest-energy event ever associated with any GRB.