%0 Journal Article %1 Aharonian2009 %A Aharonian, HESS Collaboration: F. %D 2009 %K HESS PKS2155 multiwavelength %T Simultaneous multiwavelength observations of the second exceptional gamma-ray flare of PKS 2155-304 in July 2006 %U http://arxiv.org/abs/0906.2002 %X 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.

@article{Aharonian2009, 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. }, added-at = {2009-06-13T02:34:05.000+0200}, author = {Aharonian, HESS Collaboration: F.}, biburl = {https://www.bibsonomy.org/bibtex/2aa1589324d1add3de2861a715df060f9/astravinsky}, description = {Simultaneous multiwavelength observations of the second exceptional gamma-ray flare of PKS 2155-304 in July 2006}, interhash = {05bb22193006e38ce848c7a601c76fc2}, intrahash = {aa1589324d1add3de2861a715df060f9}, keywords = {HESS PKS2155 multiwavelength}, note = {cite arxiv:0906.2002 Comment: 22 pages, 16 figures, accepted for publication in A&A}, timestamp = {2009-06-13T02:34:21.000+0200}, title = {Simultaneous multiwavelength observations of the second exceptional gamma-ray flare of PKS 2155-304 in July 2006}, url = {http://arxiv.org/abs/0906.2002}, year = 2009 }