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I. Donnarumma and V. Vittorini and S. Vercellone and E. Del Monte and M. Feroci and F. D'Ammando and L. Pacciani and A. W. Chen and M. Tavani and A. Bulgarelli and A. Giuliani and F. Longo and G. Pucella and A. Argan and G. Barbiellini and F. Boffelli and P. Caraveo and P. W. Cattaneo and V. Cocco and E. Costa and G. De Paris and G. Di Cocco and Y. Evangelista and M. Fiorini and T. Froysland and M. Frutti and F. Fuschino and M. Galli and F. Gianotti and C. Labanti and I. Lapshov and F. Lazzarotto and P. Lipari and M. Marisaldi and M. Mastropietro and S. Mereghetti and E. Morelli and A. Morselli and A. Pellizzoni and F. Perotti and P. Picozza and G. Porrovecchio and M. Prest and M. Rapisarda and A. Rappoldi and A. Rubini and P. Soffitta and M. Trifoglio and A. Trois and E. Vallazza and A. Z
Astrophysical Journal Letters
The June 2008 Flare of Markarian 421 from Optical to TeV Energies
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We present optical, X-ray, high-energy ( ##IMG## [] lap 30 GeV) and very high energy ( ##IMG## [] gap 100 GeV; VHE) observations of the high-frequency peaked blazar Mrk 421 taken between 2008 May 24 and June 23. A high-energy γ-ray signal was detected by AGILE with ##IMG## [] $\sqrtTS=4.5$ between June 9 and 15, with F ( E >100 MeV)=42 +14 –12 × 10 –8 photons cm –2 s –1 . This flaring state is brighter than the average flux observed by EGRET by a factor of ~3, but still consistent with the highest EGRET flux. In hard X-rays (20-60 keV) SuperAGILE resolved a five-day flare (June 9-15) peaking at ~55 mCrab. SuperAGILE, RXTE /ASM and Swift /BAT data show a correlated flaring structure between soft and hard X-rays. Hints of the same flaring behavior are also detected in the simultaneous optical data provided by the GASP-WEBT. A Swift /XRT observation near the flaring maximum revealed the highest 2-10 keV flux ever observed from this source, of 2.6 × 10 –9 erg cm –2 s –1 (i.e. >100 mCrab). A peak synchrotron energy of ~3 keV was derived, higher than typical values of ~0.5-1 keV. VHE observations with MAGIC and VERITAS between June 6 and 8 showed the flux peaking in a bright state, well correlated with the X-rays. This extraordinary set of simultaneous data, covering a 12-decade spectral range, allowed for a deep analysis of the spectral energy distribution as well as of correlated light curves. The γ-ray flare can be interpreted within the framework of the synchrotron self-Compton model in terms of a rapid acceleration of leptons in the jet.
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