Presentation #344.03 in the session Gamma Ray Bursts — iPoster Session.
Evidence for rapid variability during the onset of detected high-energy gamma-ray emission is found for two gamma-ray bursts (GRBs): GRB 090510 and GRB 080916C. Specifically, an analysis of photons between 30 MeV and 30 GeV as detected by the Fermi Large Area Telescope (LAT) shows variability within the first visible ‘pulse’ on the time scale of hundredths to tenths of a second, particularly for photons above 1 GeV. Chosen for the large number of high-energy photons detected and because they had known spectroscopic redshifts, both the short (GRB 090510) and long (GRB 080916C) bursts showed rapid early variability. The specific nature of this variability may provide clues about the geometry, dynamics, or even viability of some GRB models. Previously identified GRB variability at high energies and short time scales has proven useful for constraining cosmological dispersion, Lorentz-invariance violations, and weak equivalence principle violations.