Simultaneous x-ray and t[clc]e[/clc]v observations of a rapid flare from markarian 421

Maraschi, L.
Fossati, G.
Tavecchio, F.
Chiappetti, L.
Celotti, A.
Ghisellini, G.
Grandi, P.
Pian, E.
Tagliaferri, G.
Treves, A.
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Maraschi, L. Fossati, G.; Tavecchio, F.; Chiappetti, L.; Celotti, A.; Ghisellini, G.; Grandi, P.; Pian, E.; Tagliaferri, G.; Treves, A.; Breslin, A. C.; Buckley, J. H.; Carter-Lewis, D. A.; Catanese, M.; Cawley, M. F.; Fegan, D. J.; Fegan, S.; Finley, J.; Gaidos, J.; Hall, T.; Hillas, A. M.; Krennrich, F.; Lessard, R. W.; Masterson, C.; Moriarty, P.; Quinn, J.; Rose, J.; Samuelson, F.; Weekes, T. C.; Urry, C. M.; Takahashi, T. (1999). Simultaneous x-ray and t[clc]e[/clc]v observations of a rapid flare from markarian 421. The Astrophysical Journal 526 (2), L81-L84
Mrk 421 was observed for about 2 days with BeppoSAX in 1998 April as part of a worldwide multiwavelength campaign. A large, well-defined flare was observed in X-rays. The same flare was observed simultaneously at TeV energies by the Whipple Observatory gamma-ray telescope. These data provide (1) the first evidence that the X-ray and TeV intensities are well correlated on timescales of hours and (2) the first exactly simultaneous X-ray and TeV spectra. The results imply that the X-ray and TeV photons derive from the same region and from the same population of relativistic electrons. 'The physical parameters deduced from a homogeneous synchrotron self-Compton model for the spectral energy distribution yield electron cooling times close to the observed variability timescales.
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