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تسجيل مستخدم جديدBright $gamma$-ray flares observed in GRB131108A
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GRB 131108A is a bright long Gamma-Ray Burst (GRB) detected by the Large Area Telescope and the Gamma-ray Burst Monitor on board the textit{Fermi Gamma-ray Space Telescope}. Dedicated temporal and spectral analyses reveal three $gamma$-ray flares dominating above 100 MeV, which are not directly related to the prompt emission in the GBM band (10 keV--10 MeV). The high-energy light curve of GRB 131108A (100 MeV -- 10 GeV) shows an unusual evolution: a steep decay, followed by three flares with an underlying emission, and then a long-lasting decay phase. The detailed analysis of the $gamma$-ray flares finds that the three flares are 6 -- 20 times brighter than the underlying emission and are similar to each other. The fluence of each flare, (1.6 $sim$ 2.0) $times$ 10$^{-6}$ erg cm$^{-2}$, is comparable to that of emission during the steep decay phase, 1.7 $times$ 10$^{-6}$ erg cm$^{-2}$. The total fluence from three $gamma$-ray flares is 5.3 $times$ 10$^{-6}$ erg cm$^{-2}$. The three $gamma$-ray flares show properties similar to the usual X-ray flares that are sharp flux increases, occurring in $sim$ 50% of afterglows, in some cases well after the prompt emission. Also, the temporal and spectral indices during the early steep decay phase and the decaying phase of each flare show the consistency with a relation of the curvature effect ($hat{alpha}$ = 2 + $hat{beta}$), which is the first observational evidence of the high-latitude emission in the GeV energy band.
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