Simultaneous multiwavelength observations of the second exceptional gamma-ray flare of PKS2155-304 in July 2006

Aims. The X-ray-TeV connection and the evolution of the emitting particle population is studied in high-energy peaked BL Lac objects, by obtaining spectral information in both bands on sub-hour timescales. Methods. Simultaneous observations with HESS, Chandra and the Bronberg optical observatory wer...

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Veröffentlicht in:	Astronomy and astrophysics (Berlin) 2009-08, Vol.502 (3), p.749
Hauptverfasser:	Aharonian, F., Akhperjanian, A. G., Behera, B., Benbow, W., Brucker, J., Brun, P., Buehler, R., Buesching, I., Boutelier, T., Charbonnier, A., Chaves, R. C. G., Cheesebrough, A., Chounet, L. -M, Clapson, A. C., Coignet, G., Daniel, M. K., Degrange, B., Drury, L. O 'C., Dubois, F., Emmanoulopoulos, D., Farnier, C., Feinstein, F., Fiasson, A., Fontaine, G., Fuessling, M., Gallant, Y. A., Goehring, D., Heinzelmann, G., Henri, G., Hermann, G., Hinton, J. A., Hoffmann, A., Hofmann, W., Hoppe, S., Horns, D., Jacholkowska, A., de Jager, O. C., Jung, I., Katz, U., Kaufmann, S., Kendziorra, E., Kerschhaggl, M., Khangulyan, D., Keogh, D., Kluzniak, W., Komin, Nu, Kosack, K., Lamanna, G., Lenain, J. -P, Marandon, V., Martineau-Huynh, O., Marcowith, A., McComb, T. J. L., Moderski, R., Monard, L. A. G., Moulin, E., de Naurois, M., Niemiec, J., Nolan, S. J., Olive, J. -F, Wilhelmi, E. de Ona, Orford, K. J., Panter, M., Pelletier, G., Pita, S., Punch, M., Rayner, S. M., Renaud, M., Ripken, J., Rosier-Lees, S., Rowell, G., Rudak, B., Rulten, C. B., Sahakian, V., Santangelo, A., Schlickeiser, R., Schoeck, F. M., Schwanke, U., Schwarzburg, S., Schwemmer, S., Shalchi, A., Sikora, M., Skilton, J. L., Sol, H., Spangler, D., Steenkamp, R., Stegmann, C., Tavernet, J. -P, Terrier, R., Tibolla, O., Tluczykont, M., Van Eldik, C., Venter, C., Venter, L., Vialle, J. P., Vincent, P., Vivier, M., Wagner, S. J., Ward, M., Zdziarski, A. A.
Format:	Artikel
Sprache:	eng
Schlagworte:	Astroparticle Physics Astropartikelfysik galaxies: active galaxies: BL Lacertae objects: individual: PKS 2155-304 gamma rays: observations X-rays: galaxies
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Beschreibung
Zusammenfassung:	Aims. The X-ray-TeV connection and the evolution of the emitting particle population is studied in high-energy peaked BL Lac objects, by obtaining spectral information in both bands on sub-hour timescales. Methods. Simultaneous observations with HESS, Chandra and the Bronberg optical observatory were performed on the BL Lac object PKS 2155-304 in the night of July 29-30 2006, when the source underwent a major gamma-ray outburst during its high-activity state of Summer 2006. This event took place about 44 h after the other major outburst of the night of July 27-28, which is known for its ultrafast variability. An unprecedented 6 to 8 h of simultaneous, uninterrupted coverage was achieved, with spectra and light curves measured down to 7 and 2 min timescales, respectively. Results. The source exhibited one major flare along the night, at high energies. The gamma-ray flux reached a maximum of similar to 11 times the Crab flux (>400 GeV), with rise/decay timescales of similar to 1 h, plus a few smaller-amplitude flares superimposed on the decaying phase. The emission in the X-ray and VHE gamma-ray bands is strongly correlated, with no evidence of lags. The spectra also evolve with similar patterns, and are always soft ( photon index G > 2), indicating no strong shift of the peaks in the spectral energy distribution towards higher energies. Only at the flare maximum is there evidence that the gamma-ray peak is inside the observed passband, at similar to 400-600 GeV. The VHE spectrum shows a curvature that is variable with time and stronger at higher fluxes. The huge VHE variations (similar to 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 a high-energy peaked BL Lac object a large Compton dominance (L(C)/L(S) similar to 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.
ISSN:	0004-6361 1432-0746
DOI:	10.1051/0004-6361/200912128