Baring, M.G.Axelsson, M.Baldini, L.Barbiellini, G.Bellazzini, R.Bregeon, J.Brigida, M.Bruel, P.Buehler, R.Caliandro, G.A.Cameron, R.A.Caraveo, P.A.Cecchi, C.Chaves, R.C.G.Chekhtman, A.Chiang, J.Claus, R.Conrad, J.Cutini, S.D'Ammando, F.de Palma, F.Dermer, C.D.do Couto e Silva, E.Drell, P.S.Favuzzi, C.Fegan, S.J.Ferrara, E.C.Focke, W.B.Fukazawa, Y.Fusco, P.Gargano, F.Gasparrini, D.Gehrels, N.Germani, S.Giglietto, N.Giroletti, M.Godfrey, G.Guiriec, S.Hadasch, D.Hanabata, Y.Hayashida, M.Hou, X.Iyyani, S.Jackson, M.S.Kocevski, D.Kuss, M.Larsson, J.Longo, F.Loparco, F.Lundman, C.Mazziotta, M.N.McEnery, J.E.Mizuno, T.Monzani, M.E.Moretti, E.Morselli, A.Murgia, S.Nuss, E.Nymark, T.Ohno, M.Omodei, N.Pesce-Rollins, M.Piron, F.Pivato, G.Racusin, J.L.Rainò, S.Razzano, M.Razzaque, S.Reimer, A.Roth, M.Ryde, F.Sanchez, D.A.Sgrò, C.Siskind, E.J.Spandre, G.Spinelli, P.Stamatikos, M.Tibaldo, L.Tinivella, M.Usher, T.L.Vandenbroucke, J.Vasileiou, V.Vianello, G.Vitale, V.Waite, A.P.Winer, B.L.Wood, K.S.Burgess, J.M.Bhat, P.N.Bissaldi, E.Briggs, M.S.Connaughton, V.Fishman, G.Fitzpatrick, G.Foley, S.Gruber, D.Kippen, R.M.Kouveliotou, C.Jenke, P.McBreen, S.McGlynn, S.Meegan, C.Paciesas, W.S.Pelassa, V.Preece, R.Tierney, D.von Kienlin, A.Wilson-Hodge, C.Xiong, S.Pe'er, A.Pe'er, A.2013-03-142014-03-192012Baring, M.G., Axelsson, M., Baldini, L., et al.. "GRB110721A: An Extreme Peak Energy and Signatures of the Photosphere." <i>The Astrophysical Journal Letters,</i> 757, (2012) The American Astronomical Society: L31. http://dx.doi.org/10.1088/2041-8205/757/2/L31.https://hdl.handle.net/1911/70582GRB110721A was observed by the Fermi Gamma-ray Space Telescope using its two instruments, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). The burst consisted of one major emission episode which lasted for ~24.5 s (in the GBM) and had a peak flux of (5.7 ± 0.2) × 10–5 erg s–1 cm–2. The time-resolved emission spectrum is best modeled with a combination of a Band function and a blackbody spectrum. The peak energy of the Band component was initially 15 ± 2 MeV, which is the highest value ever detected in a GRB. This measurement was made possible by combining GBM/BGO data with LAT Low Energy events to achieve continuous 10-100 MeV coverage. The peak energy later decreased as a power law in time with an index of –1.89 ± 0.10. The temperature of the blackbody component also decreased, starting from ~80 keV, and the decay showed a significant break after ~2 s. The spectrum provides strong constraints on the standard synchrotron model, indicating that alternative mechanisms may give rise to the emission at these energies.engArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.Journal articlegamma-ray burst: generalgamma-ray burst: individual (GRB110721A)radiation mechanisms: thermalhttp://dx.doi.org/10.1088/2041-8205/757/2/L31