摘要
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. γγ 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 Ecutoff depends on the photon index/3 and the cutoff occurs at very high energy, Ecutoff = 161＋533 GeV in GRB 080916C and Ecutoff ≥ 100 GeV （forβ ≈-2.3） in GRB 090926A. Such high energy photons, if they exist, may disfavor the synchrotron origin and need alternative generation mechanisms.
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. γγ 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 Ecutoff depends on the photon index/3 and the cutoff occurs at very high energy, Ecutoff = 161＋533 GeV in GRB 080916C and Ecutoff ≥ 100 GeV （forβ ≈-2.3） in GRB 090926A. Such high energy photons, if they exist, may disfavor the synchrotron origin and need alternative generation mechanisms.
基金
supported by the Open Research Program of the Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences
