中国科学院云南天文台机构知识库

It is expected that there should be a spectral cutoff at the high energy end of emission from a prompt gamma-ray burst (GRB), due to, e.g. gamma gamma absorption and/or a high energy cutoff in the electron distribution. We analyze the spectral data of Fermi-LAT detected GRBs 080916C and 090926A, aiming at locating the spectral cutoff. By assuming that the prompt GRB spectrum at the high energy end is a power law with an exponential cutoff, our analysis finds that the cutoff energy E-cutoff depends on the photon index beta and the cutoff occurs at very high energy, E-cutoff = 161(-95)(+533) GeV in GRB 080916C and E-cutoff greater than or similar to 100 GeV (for beta approximate to -2.3) in GRB 090926A. Such high energy photons, if they exist, may disfavor the synchrotron origin and need alternative generation mechanisms.