The June 2008 Flare of Markarian 421 from Optical to TeV Energies

I. DONNARUMMA ET AL. SON 295 AUTORES. A. PICHEL

ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES

IOP PUBLISHING LTD

Año: 2009 vol. 691L p. 13 - 19

0067-0049

We present optical, X-ray, high energy (=100 GeV; VHE) observations of the high-frequency peaked blazar Mrk 421 taken between 2008 May 24 and June 23. A high energy -ray signal was detected by AGILE with (TS)^(1/2) = 4.5 on June 9-15, 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 5-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 on June 6-8 show the flux peaking in a bright state, well correlated with the X-rays. This extraordinary set of simultaneous data, covering a twelve-decade spectral range, allowed for a deep analysis of the spectral energy distribution as well as of correlated light curves. The gamma-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.