Speaker
Description
In 2022, GRB221009A was detected by the LHAASO collaboration as the brightest gamma-ray burst (GRB) ever recorded with photon energies that extended up to 18TeV. Combined with the redshift of $z=0.151$ of the GRB, it has been questioned whether these observations can be reconciled with standard physics, since such high energy photons suffer from absorption on the extragalactic background light (EBL). A possible explanation could be the oscillation between gamma rays and hypothetical axion-like particles (ALPs), which would effectively lower the absorption. Here, we analyze LHAASO data from GRB221009A using a maximum likelihood approach. We consider different magnetic-field scenarios for photon-ALP conversion and test different EBL models. We find that models including photon-ALP oscillations are not significantly preferred and we conclude that ALPs are generally not required to explain the LHAASO observations of GRB221009A. Instead, we are able to set competitive constraints on the photon-ALP coupling.