R. Buehler, J. D. Scargle, R. D. Blandford, L. Baldini, M. G. Baring, A. Belfiore, E. Charles, J. Chiang, F. D'Ammando, C. D. Dermer, S. Funk, J. E. Grove, A. K. Harding, E. Hays, M. Kerr, F. Massaro, M. N. Mazziotta, R. W. Romani, P. M. Saz Parkinson, A. F. Tennant, M. C. Weisskopf
The Large Area Telescope on board the Fermi satellite observed a gamma-ray
flare in the Crab nebula lasting for approximately nine days in April of 2011.
The source, which at optical wavelengths has a size of \approx 11 ly across,
doubled its gamma-ray flux within eight hours. The peak photon flux was (186
\pm 6) \times 10-7 cm-2 s-1 above 100 MeV, which corresponds to a 30-fold
increase compared to the average value. During the flare, a new component
emerged in the spectral energy distribution, which peaked at an energy of (375
\pm 26) MeV at flare maximum. The observations imply that the emission region
was relativistically beamed toward us and that variations in its motion are
responsible for the observed spectral variability.
View original:
http://arxiv.org/abs/1112.1979
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