An Exceptional VHE Gamma-Ray Flare of PKS 2155-304

F. Aharonian , A.G. Akhperjanian , A.R. Bazer-Bachi (1) , M. Beilicke , W. Benbow , D. Berge , K. Bernlöhr , C. Boisson (2) , O. Bolz , V. Borrel , I. Braun , E. Brion (3) , A. M. Brown , R. Buhler , I. Busching , T. Boutelier , S. Carrigan , P.M. Chadwick , L.M. Chounet (4) , G. Coignet (5) , R. Cornils , L. Costamante , B. Degrange (4) , H.J. Dickinson , A. Djannati-Ataï (6) , L. O'Connor-Drury , G. Dubus (4) , K. Egberts , D. Emmanoulopoulos , P. Espigat (7) , C. Farnier (8) , F. Feinstein (8) , E. Ferrero , A. Fiasson (8) , G. Fontaine (4) , S. Funk , M. Fuling , Y.A. Gallant (8) , B. Giebels (4) , J.F. Glicenstein (3) , B. Glück , P. Goret (3) , C. Hadjichristidis , D. Hauser , M. Hauser , G. Heinzelmann , G. Henri , G. Hermann , J. A. Hinton , A. Hoffmann , W. Hofmann , M. Holleran , S. Hoppe , D. Horns , A. Jacholkowska (8) , O.C. de Jager , E. Kendziorra , M. Kerschhaggl , B. Khelifi (4) , N. Komin (8) , K. Kosack , G. Lamanna (5) , I. J. Latham , R. Le Gallou , A. Lemiere (7) , M. Lemoine-Goumard (4) , T. Lohse , J.M. Martin (2) , O. Martineau-Huynh (9) , A. Marcowith (1, 8) , C. Masterson , G. Maurin (7) , T.J.L. Mccomb , Emmanuel Moulin (3, 8) , M. de Naurois , D. Nedbal , S.J. Nolan , A. Noutsos , J.P. Olive (1) , K.J. Orford , J.L. Osborne , M. Panter , G. Pelletier , P.O. Petrucci (10) , S. Pita (7) , G. Pühlhofer , M. Punch (7) , S. Ranchon (5) , B.C. Raubenheimer , M. Raue , S.M. Rayner , A. Reimer , O. Reimer , J. Ripken , L. Rob , L. Rolland (3) , S. Rosier-Lees (5) , G. Rowell , V.V. Sahakian , A. Santangelo , L. Sauge , S. Schlenker , R. Schlickeiser , R. Schröder , U. Schwanke , S. Schwarzburg , S. Schwemmer , A. Shalchi , H. Sol (2) , D. Spangler , F. Spanier , R. Steenkamp , C. Stegmann , G. Superina (4) , P.H. Tam , J.P. Tavernet (9) , R. Terrier (7) , M. Tluczykont (4) , C. van Eldik , G. Vasileiadis (8) , C. Venter , J.P. Vialle (5) , P. Vincent (9) , H.J. Völk , S.J. Wagner , M. Ward

1 CESR - Centre d'étude spatiale des rayonnements
2 LUTH (UMR_8102) - Laboratoire Univers et Théories
3 DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
4 LLR - Laboratoire Leprince-Ringuet
5 LAPP - Laboratoire d'Annecy de Physique des Particules
6 APC - AHE - APC - Astrophysique des Hautes Energies
7 APC (UMR_7164) - AstroParticule et Cosmologie
8 LPTA - Laboratoire de Physique Théorique et Astroparticules
9 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
10 LAOG - Laboratoire d'Astrophysique de Grenoble

The high-frequency peaked BL Lac PKS 2155-304 at redshift z=0.116 is a well-known VHE (>100 GeV) gamma-ray emitter. Since 2002 its VHE flux has been monitored using the H.E.S.S. stereoscopic array of imaging atmospheric-Cherenkov telescopes in Namibia. During the July 2006 dark period, the average VHE flux was measured to be more than ten times typical values observed from the object. This article focuses solely on an extreme gamma-ray outburst detected in the early hours of July 28, 2006 (MJD 53944). The average flux observed during this outburst is I(>200 GeV) = (1.72$\pm$$0.05_{\rm stat}$$\pm$$0.34_{\rm syst}$) $\times$ 10$^{-9}$ cm$^{-2}$ s$^{-1}$, corresponding to ~7 times the flux, I(>200 GeV), observed from the Crab Nebula. Peak fluxes are measured with one-minute time scale resolution at more than twice this average value. Variability is seen up to ~600 s in the Fourier power spectrum, and well-resolved bursts varying on time scales of ~200 seconds are observed. There are no strong indications for spectral variability within the data. Assuming the emission region has a size comparable to the Schwarzschild radius of a ~10$^9 M_\odot$ black hole, Doppler factors greater than 100 are required to accommodate the observed variability time scales.

Mots clés: Galaxies: active; BL Lacertae objects: Individual: PKS 2155−304; Gamma rays: observations

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]

F. Aharonian, A.G. Akhperjanian, A.R. Bazer-Bachi, M. Beilicke, W. Benbow, et al.. An Exceptional VHE Gamma-Ray Flare of PKS 2155-304. The Astrophysical journal letters, 2007, 664, pp.L71-L74. ⟨10.1086/520635⟩. ⟨in2p3-00152627⟩