Detection of extended very-high-energy gamma-ray emission towards the young stellar cluster Westerlund 2

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 (1) , I. Braun , E. Brion , A. M. Brown , R. Buhler , I. Busching , T. Boutelier (3) , 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 (9) , B. Glück , P. Goret (9) , C. Hadjichristidis , D. Hauser , M. Hauser , G. Heinzelmann , G. Henri (3) , 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 (10) , A. Marcowith (1, 8) , C. Masterson , G. Maurin (7) , T. J. L. Mccomb , Emmanuel Moulin (8) , M. de Maurois (10) , D. Nedbal , S. J. Nolan , A. Noutsos , J. P. Olive , K. J. Orford , J. L. Osborne , M. Panter , G. Pelletier (3) , P. O. Petrucci (3) , 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 (9) , S. Rosier-Lees (5) , G. Rowell , V. V. Sahakian , A. Santangelo , L. Sauge (3) , 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 (10) , R. Terrier (7) , M. Tluczykont (4) , C. van Eldik , G. Vasileiadis (8) , C. Venter , J. P. Vialle (5) , P. Vincent (10) , 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 LAOG - Laboratoire d'Astrophysique de Grenoble
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 DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
10 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies

Results from gamma-ray observations by the H.E.S.S. telescope array in the direction of the young stellar cluster Westerlund 2 are presented. Stereoscopic imaging of Cherenkov light emission of gamma-ray induced showers in the atmosphere is used to study the celestial region around the massive Wolf-Rayet (WR) binary WR 20a. Spectral and positional analysis is performed using standard event reconstruction techniques and parameter cuts. The detection of a new gamma-ray source is reported from H.E.S.S. observations in 2006. HESS J1023-575 is found to be coincident with the young stellar cluster Westerlund 2 in the well-known HII complex RCW 49. The source is detected with a statistical significance of more than 9 sigma, and shows extension beyond a point-like object within the H.E.S.S. point-spread function. The differential gamma-ray spectrum of the emission region is measured over approximately two orders of magnitude in flux. The spatial coincidence between HESS J1023-575 and the young open cluster Westerlund 2, hosting e.g. the massive WR binary WR 20a, requires a look into a variety of potential models to account for the observed very-high-energy (VHE) gamma-ray emission. Considered emission scenarios include emission from the colliding wind zone of WR 20a, collective stellar winds from the extraordinary ensemble of hot and massive stars in the stellar cluster Westerlund 2, diffusive shock acceleration in the wind-blown bubble itself, and supersonic winds breaking out into the interstellar medium (ISM). The observed source extension argues against a single star origin of the observed VHE emission.

Mots clés: ISM: star forming regions; ISM: individual objects: HESS J1023-575; WR 20a; RCW 49 (NGC 3247; G284.3-0.3); 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.. Detection of extended very-high-energy gamma-ray emission towards the young stellar cluster Westerlund 2. Astronomy and Astrophysics - A&A, 2007, 467, pp.1075-1080. ⟨10.1051/0004-6361:20066950⟩. ⟨in2p3-00142313⟩