  Recently an extraordinarily bright gamma-ray burst, GRB 221009A, was observed
by several facilities covering the whole electromagnetic spectrum. Gamma rays
with energies up to 18 TeV were detected, as well as a possible photon with 251
TeV. Such energetic events are not expected because they would be attenuated by
pair-production interactions with the extragalactic background light. This
tension is, however, only apparent, and does not call for any unconventional
explanation. Here I show that these observations can be interpreted as the
result of ultra-high-energy cosmic rays (UHECRs) interacting with cosmological
radiation fields during their journey to Earth, provided that intergalactic
magnetic fields are reasonably weak. If this hypothesis is correct, it would
establish bursts like GRB 221009A as UHECR sources.
