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Abstract: The Fermi Gamma-Ray Space Telescope has more than doubled the number ofGamma-Ray Bursts GRBs detected above 100 MeV within its first year ofoperation. Thanks to the very wide energy range covered by Fermi-s Gamma-rayBurst Monitor GBM; 8 keV to 40 MeV and Large Area Telescope LAT; 25 MeV to>300 GeV it has measured the prompt GRB emission spectrum over anunprecedentedly large energy range from ~8 keV to ~30 GeV. Here I brieflyoutline some highlights from Fermi GRB observations during its first ~1.5 yr ofoperation, focusing on the prompt emission phase. Interesting new observationsare discussed along with some of their possible implications, including: iWhat can we learn from the Fermi-LAT GRB detection rate, ii A limit on thevariation of the speed of light with photon energy for the first time beyondthe Planck scale for a linear energy dependence from direct time of arrivalmeasurements, iii Lower-limits on the bulk Lorentz factor of the GRB outflowof ~1000 for the brightest Fermi LAT GRBs, iv The detection or in othercases, lack thereof of a distinct spectral component at high and sometimesalso at low energies, and possible implications for the prompt GRB emissionmechanism, v The later onset and longer duration of the high-energyemission >100 MeV, compared to the low-energy < ~1 MeV emission, that isseen in most Fermi-LAT GRBs.



Author: Jonathan Granot, for the Fermi LAT Collaboration, the GBM Collaboration

Source: https://arxiv.org/



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