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 Fermi Gamma-ray Space Telescope. Dedicated temporal and spectral analyses reveal three γ-ray flares dominating above 100 MeV, which are not directly related to the prompt emission in the Gamma-ray Burst Monitor 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 γ-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 ∼ 2.0) × 10-6 erg cm-2, is comparable to that of emission during the steep decay phase, 1.7 × 10-6 erg cm-2. The total fluence from three γ-ray flares is 5.3 × 10-6 erg cm-2. The three γ-ray flares show properties similar to the usual X-ray flares that are sharp flux increases, occurring in ∼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{α } = 2 + \hat{β }), which is the first observational evidence of the high-latitude emission in the GeV energy band.
Bright $\gamma$-ray flares observed in GRB131108A / Ajello, M.; Arimoto, M.; Asano, K.; Axelsson, M.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Berretta, A.; Bissaldi, E.; D. Blandford, R.; Bonino, R.; Bottacini, E.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; A. Cameron, R.; Caputo, R.; A. Caraveo, P.; Cavazzuti, E.; Chen, S.; Chiaro, G.; Ciprini, S.; Costantin, D.; Cutini, S.; D'Ammando, F.; de la Torre Luque, P.; de Palma, F.; Di Lalla, N.; Di Venere, L.; Fana Dirirsa, F.; J. Fegan, S.; Franckowiak, A.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giordano, F.; Giroletti, M.; Green, D.; A. Grenier, I.; Grondin, M. -H.; Guiriec, S.; Hays, E.; Horan, D.; J 'ohannesson, G.; Kocevski, D.; Kovac'Evic', M.; Kuss, M.; Larsson, S.; Latronico, L.; Li, J.; Liodakis, I.; Longo, F.; Loparco, F.; N. Lovellette, M.; Lubrano, P.; Maldera, S.; Manfreda, A.; Mart 'i-Devesa, G.; N. Mazziotta, M.; E. McEnery, J.; F. Michelson, P.; Mizuno, T.; E. Monzani, M.; Moretti, E.; Morselli, A.; V. Moskalenko, I.; Negro, M.; Nuss, E.; Ohno, M.; Omodei, N.; Orienti, M.; Orlando, E.; Palatiello, M.; S. Paliya, V.; Paneque, D.; Pei, Z.; Persic, M.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Poon, H.; A. Porter, T.; Principe, G.; L. Racusin, J.; Rain `o, S.; Rando, R.; Rani, B.; Razzano, M.; Reimer, A.; Reimer, O.; Serini, D.; Sgr `o, C.; J. Siskind, E.; Spandre, G.; Spinelli, P.; Tajima, H.; Takagi, K.; Tak, D.; F. Torres, D.; Valverde, J.; Wood, K.; Yamazaki, R.; Yassine, M.; Zhu, S.; Uhm, Z. L.; Zhang, B.. - In: THE ASTROPHYSICAL JOURNAL LETTERS. - ISSN 2041-8205. - (2019), pp. ---.
Bright $\gamma$-ray flares observed in GRB131108A
Longo, F.;Orlando, E.;Palatiello, M.;Principe, G.;
2019-01-01
Abstract
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 Fermi Gamma-ray Space Telescope. Dedicated temporal and spectral analyses reveal three γ-ray flares dominating above 100 MeV, which are not directly related to the prompt emission in the Gamma-ray Burst Monitor 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 γ-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 ∼ 2.0) × 10-6 erg cm-2, is comparable to that of emission during the steep decay phase, 1.7 × 10-6 erg cm-2. The total fluence from three γ-ray flares is 5.3 × 10-6 erg cm-2. The three γ-ray flares show properties similar to the usual X-ray flares that are sharp flux increases, occurring in ∼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{α } = 2 + \hat{β }), which is the first observational evidence of the high-latitude emission in the GeV energy band.Pubblicazioni consigliate
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