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The tera-electronvolt (TeV) light curve of gamma-ray burst (GRB) 221009Ashows an unprecedentedly rapid rise at the beginning epoch. This phenomenoncould be due to the strong absorption of photons and electrons within theemitting region. As the external shock expands outwards and the radiusincreases, the volume of matter also increases, leading to a gradual decreasein the optical depth for TeV photons. We explore several possibilities for thephysical origin of this peculiar behavior. We calculate the optical depth forTeV photons due to annihilation with lower energy photons in the external shockand scattering by electrons produced via cascading of the TeV emission. Evenunder aggressive assumptions, we find the optical depths for these processesare orders of magnitude too small to explain the observed light curve. Othersources of absorbers, such as electrons in the ejecta or external shock, alsodo not yield sufficient optical depths. Therefore, the origin of the earlypeculiar TeV light curve remains uncertain.

What absorbs the early TeV photons of GRB 221009A?