Kouveliotou, C.16; Granot, J.17; Racusin, J. L.18; Bellm, E.19; Vianello, G.7; Oates, S.8; Fryer, C. L.9; Boggs, S. E.10; Christensen, Finn Erland1; Craig, W. W.10; Dermer, C. D.11; Gehrels, N.18; Hailey, C. J.20; Harrison, F. A.19; Melandri, A.13; McEnery, J. E.18; Mundell, C. G.21; Stern, D. K.15; Tagliaferri, G.13; Zhang, W. W.18
1 National Space Institute, Technical University of Denmark2 Astrophysics, National Space Institute, Technical University of Denmark3 NASA Marshall Space Flight Center4 Open University of Israel5 NASA Goddard Space Flight Center6 California Institute of Technology7 Stanford University8 University College London9 Los Alamos National Laboratory10 University of California11 National Research Laboratory12 Columbia University13 National Institute for Astrophysics14 Liverpool John Moores University15 NASA Jet Propulsion Laboratory16 NASA Marshall Space Flight Center17 Open University of Israel18 NASA Goddard Space Flight Center19 California Institute of Technology20 Columbia University21 Liverpool John Moores University
GRB 130427A occurred in a relatively nearby galaxy; its prompt emission had the largest GRB fluence ever recorded. The afterglow of GRB 130427A was bright enough for the Nuclear Spectroscopic Telescope ARray (NuSTAR) to observe it in the 3-79 keV energy range long after its prompt emission (similar to 1.5 and 5 days). This range, where afterglow observations were previously not possible, bridges an important spectral gap. Combined with Swift, Fermi, and ground-based optical data, NuSTAR observations unambiguously establish a single afterglow spectral component from optical to multi-GeV energies a day after the event, which is almost certainly synchrotron radiation. Such an origin of the late-time Fermi/Large Area Telescope >10 GeV photons requires revisions in our understanding of collisionless relativistic shock physics.