PKS 2155-304 in July 2006: H.E.S.S. results and simultaneous multi-wavelength observations.

The high-frequency-peaked BL Lac PKS 2155-304 is one of the brightest and best-studied VHE γ-ray sources in the southern hemisphere. The High Energy Stereoscopic System (H.E.S.S.) has monitored PKS 2155-304 in 2006 and a multi-wavelength campaign involving X-ray, optical and radio observatories was triggered by the detection of an active state in July 2006, followed by the detection of two extraordinary flares on July, 28th and 30th, with peak fluxes ∼100 times the usual values. We present results from the spectral and flux variability analysis of the VHE and simultaneous X-ray observations with Chandra during the second flare, as well as the detailed evolution of the VHE flux of PKS 2155-304 observed by H.E.S.S. in 2006. A study of flux correlations in the different frequency ranges during the second flare and the adjacent nights is discussed. We also present an interpretation of the active state of PKS 2155-304 in the framework of synchrotron self-Compton emission. [ABSTRACT FROM AUTHOR]