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Type: Journal article
Title: Simultaneous multiwavelength observations of the second exceptional gamma-ray flare of PKS2155-304 in July 2006
Author: Rowell, G.
Citation: Astronomy and Astrophysics: a European journal, 2009; 502(3):749-770
Publisher: E D P Sciences
Issue Date: 2009
ISSN: 0004-6361
Statement of
F. Aharonian...G. Rowell...and A. Zech et al.(HESS Collaboration)
Abstract: Simultaneous HESS/CHANDRA/optical observations were performed on the BL Lac object PKS 2155-304 in the night of July 29-30 2006, when the source underwent its second major gamma-ray outburst in Summer 2006. This event took place about 44 hours after the July 28 outburst, known for its ultrafast variability. An unprecedented 6 to 8 hours of uninterrupted coverage was achieved, with spectra and light curves measured down to 7 and 2-minute timescales, respectively. The gamma-ray flux reached a maximum of 11x the Crab flux (>400 GeV), with rise/decay timescales of ~1 hour, plus a few smaller-amplitude flares superimposed on the decaying phase. The emission in the X-ray and VHE bands is strongly correlated, both in flux and spectrum, with no evidence of lags. The VHE spectrum shows a curvature that is variable with time and stronger at higher fluxes. The huge VHE variations (22x) are only accompanied by small-amplitude X-ray and optical variations (factor 2 and 15% respectively). The source has shown for the first time in an HBL a large Compton dominance (L_C/L_S ~10) -- rapidly evolving -- and a cubic relation between VHE and X-ray flux variations, during a decaying phase. These results challenge the common scenarios for the TeV-blazar emission.
Keywords: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Rights: © ESO 2009. Submitted to Cornell University’s online archive in 2009 by Luigi Costamante. Post-print sourced from
DOI: 10.1051/0004-6361/200912128
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