Bright Gamma-Ray Flares Observed in GRB 131108A

Journal Article · 26 November 2019 · The Astrophysical Journal. Letters (Online)

DOI: https://doi.org/10.3847/2041-8213/ab564f · OSTI ID:1595251

Ajello, M. ; Arimoto, M. ; Asano, K.; Axelsson, M. ; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Berretta, A.; Bissaldi, E.; Blandford, R. D.; Bonino, R.; Bottacini, E.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Cameron, R. A.; Caputo, R.; Caraveo, P. A. ; Cavazzuti, E.; Chen, S.; Chiaro, G.; Ciprini, S.; Costantin, D.; Cutini, S.; D’Ammando, F. ; Torre Luque, P. de la; Palma, F. de; Lalla, N. Di; Venere, L. Di; Dirirsa, F. Fana; Fegan, S. J.; Franckowiak, A. ; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giordano, F.; Giroletti, M.; Green, D.; Grenier, I. A.; Grondin, M. -H.; Guiriec, S.; Hays, E.; Horan, D.; Jóhannesson, G.; Kocevski, D.; Kovac’evic’, M.; Kuss, M. ; Larsson, S. ; Latronico, L.; Li, J.; Liodakis, I.; Longo, F. ; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Maldera, S. ; Manfreda, A.; Martí-Devesa, G.; Mazziotta, M. N.; McEnery, J. E.; Mereu, I.; Michelson, P. F.; Mizuno, T. ; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V. ; Negro, M.; Nuss, E.; Ohno, M.; Omodei, N.; Orienti, M.; Orlando, E.; Palatiello, M.; Paliya, V. S. ; Paneque, D.; Pei, Z.; Persic, M.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Poon, H.; Porter, T. A.; Principe, G.; Racusin, J. L. ; Rainò, S.; Rando, R.; Rani, B.; Razzano, M.; Reimer, A.; Reimer, O.; Serini, D.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Tajima, H.; Takagi, K.; Tak, D.; Torres, D. F.; Valverde, J.; Wood, K.; Yamazaki, R. ; Yassine, M.; Zhu, S.; Uhm, Z. Lucas; Zhang, Bing

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. Finally, 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.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: USDOE
• Contributing Organization: Fermi-LAT Collaboration
• Grant/Contract Number: AC02-76SF00515; AC02-76SF00515
• OSTI ID: 1595251
• Journal Information: The Astrophysical Journal. Letters (Online), Journal Name: The Astrophysical Journal. Letters (Online) Journal Issue: 2 Vol. 886; ISSN 2041-8213
• Publisher: Institute of Physics (IOP)Copyright Statement
• Country of Publication: United States
• Language: English