On ALP scenarios and GRB 221009A

Understand

The extraordinarily bright gamma-ray burst GRB 221009A was observed by a large number of observatories, from radio frequencies to gamma-rays.

• Of particular interest are the reported observations of photon-like air showers of very high energy: an 18 TeV event in LHAASO and a 251 TeV event at Carpet-2.
• Gamma rays at these energies are expected to be absorbed by pair-production events on background photons when travelling intergalactic distances.
• Several works have sought to explain the observations of these events, assuming they originate from GRB 221009A, by invoking axion-like particles (ALPs).