The June 2008 flare of Markarian 421 from optical to TeV energies
Donnarumma, I. ; Vittorini, V. ; Vercellone, S. ; Giommi, P. ; Colafrancesco, S. ; Salotti, L. ; et al.
Jan - 2009
DOI: 10.1088/0004-637X/691/1/L13
ISSN : 0004-637X ;
journal : The Astrophysical Journal

Volume : 691 ; Issue : 1
type: Article Journal

Abstract
We present optical, X-ray, high-energy (30 GeV) and very 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 ³-ray signal was detected by AGILE with between June 9 and 15, with F(E>100 MeV) = 42+14 12 × 108 photons cm2 s1. 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 × 109 erg cm2 s1 (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 ³-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.

keywords : BL Lacertae objects: individual (Mrk 421); gamma rays: observations; galaxies: jets; radiation mechanisms: non-thermal; X-rays: galaxies