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American Astronomical Society, Astrophysical Journal, 1(691), p. L13-L19, 2008

DOI: 10.1088/0004-637x/691/1/l13

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The JUNE 2008 FLARE OF MARKARIAN 421 FROM OPTICAL TO TeV ENERGIES

Journal article published in 2008 by G. de Paris, A. de Angelis, E. de Cea del Pozo, B. de Lotto, M. de Maria, F. de Sabata, Chen Wp, Chow Yc, Larionov Vm, A. Zambra, D. Zanello, R. de los Reyes, R.~M M. Wagner, W. Wittek, V. Zabalza and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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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 $γ$-ray signal was detected by AGILE with \sqrt{TS}=4.5 on June 9--15, with $F(E>100 \mathrm{MeV})= 42^{+14}_{-12}\times 10^{-8}$ 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 $\times 10^{-9}$ 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 $γ$-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. ; Comment: accepted for publication in ApJL, 7 pages, 2 figures, 1 table