GRB 221009A Gamma Rays from Radiative Decay of Heavy Neutrinos?

Abstract

We consider a mechanism which allows to decrease attenuation of high energy gamma ray flux from gamma ray burst GRB 221009A. The mechanism is based on the existence of a heavy $m_N\sim0.1\,\mathrm{MeV}$ mostly sterile neutrino $N$ which mixes with active neutrinos. $N$'s are produced in GRB in $\pi$ and $K$ decays via mixing with $\nu_\mu$. They undergo the radiative decay $N\rightarrow \nu \gamma$ on the way to the Earth. The usual exponential attenuation of gamma rays is lifted to an attenuation inverse in the optical depth. Various restrictions on this scenario are discussed. We find that the high energy $\gamma$ events at $18\,\mathrm{TeV}$ and potentially $251\,\mathrm{TeV}$ can be explained if (i) the GRB active neutrino fluence is close to the observed limit, (ii) the branching ratio of $N\rightarrow \nu \gamma$ is at least of the order 10%.