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- Simultaneous multiwavelength observations of the second exceptional gamma-ray flare of PKS 2155-304 in July 2006 doi link

Author(s): Aharonian F., Bazer-Bachi A.R., Becherini Y., Boisson C., Borrel V., Boutelier T., Brion E., Brun P., Charbonnier A., Chounet L.-M., Coignet G., Degrange B., Djannati-Ataï A., Dubois F., Dubus G., Espigat P., Farnier C., Feinstein F., Fiasson A., Fontaine G., Gallant Y., Gérard L., Giebels B., Glicenstein J.F., Goret P., Henri G., Jacholkowska A., Khélifi B., Marcowith A., Vasileiadis G.

(Article) Published: Astronomy & Astrophysics, vol. 502 p.749-770 (2009)
Links openAccess full text : arxiv


Ref HAL: in2p3-00410643_v1
Ref Arxiv: 0906.2002
DOI: 10.1051/0004-6361/200912128
Ref. & Cit.: NASA ADS
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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.



Comments: 22 pages, 16 figures, accepted for publication in A&A