HAL : in2p3-00142313, version 1

arXiv : astro-ph/0703427

Code Bibliographique ADS : 2007astro.ph..3427H

DOI : 10.1051/0004-6361:20066950

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Astronomy and Astrophysics 467 (2007) 1075-1080

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

F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bachi1, M. Beilicke, W. Benbow, D. Berge, K. Bernlöhr, C. Boisson2, O. Bolz, V. Borrel1, I. Braun, E. Brion, A. M. Brown, R. Buhler, I. Busching, T. Boutelier3, S. Carrigan, P. M. Chadwick, L. M. Chounet4, G. Coignet5, R. Cornils, L. Costamante, B. Degrange4, H. J. Dickinson, A. Djannati-Ataï6, L. O'Connor-Drury, G. Dubus4, K. Egberts, D. Emmanoulopoulos, P. Espigat6, C. Farnier7, F. Feinstein7, E. Ferrero, A. Fiasson7, G. Fontaine4, S. Funk, M. Fuling, Y. A. Gallant7, B. Giebels4, J. F. Glicenstein8, B. Glück, P. Goret8, C. Hadjichristidis, D. Hauser, M. Hauser, G. Heinzelmann, G. Henri3, G. Hermann, J. A. Hinton, A. Hoffmann, W. Hofmann, M. Holleran, S. Hoppe, D. Horns, A. Jacholkowska7, O. C. De Jager, E. Kendziorra, M. Kerschhaggl, B. Khelifi4, N. Komin7, K. Kosack, G. Lamanna5, I. J. Latham, R. Le Gallou, A. Lemiere6, M. Lemoine-Goumard4, T. Lohse, J. M. Martin2, O. Martineau-Huynh9, A. Marcowith1, 7, C. Masterson, G. Maurin6, T. J. L. Mccomb, E. Moulin7, M. De Maurois9, D. Nedbal, S. J. Nolan, A. Noutsos, J. P. Olive, K. J. Orford, J. L. Osborne, M. Panter, G. Pelletier3, P. O. Petrucci3, S. Pita6, G. Pühlhofer, M. Punch6, S. Ranchon5, B. C. Raubenheimer, M. Raue, S. M. Rayner, A. Reimer, O. Reimer, J. Ripken, L. Rob, L. Rolland8, S. Rosier-Lees5, G. Rowell, V. V. Sahakian, A. Santangelo, L. Sauge3, S. Schlenker, R. Schlickeiser, R. Schröder, U. Schwanke, S. Schwarzburg, S. Schwemmer, A. Shalchi, H. Sol2, D. Spangler, F. Spanier, R. Steenkamp, C. Stegmann, G. Superina4, P. H. Tam, J. P. Tavernet9, R. Terrier6, M. Tluczykont4, C. Van Eldik, G. Vasileiadis7, C. Venter, J. P. Vialle5, P. Vincent9, H. J. Völk, S. J. Wagner, M. Ward

HESS Collaboration(s)

(2007)

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.

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

équipe(s) de recherche : APC - AHE

Thème(s)

:

Physique/Astrophysique/Cosmologie et astrophysique extra-galactique Planète et Univers/Astrophysique/Cosmologie et astrophysique extra-galactique Planète et Univers/Astrophysique

Mot(s)-clé(s) : ISM: star forming regions – ISM: individual objects: HESS J1023-575 – WR 20a – RCW 49 (NGC 3247 – G284.3-0.3) – gamma rays: observations

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Contributeur : Simone Lantz <>

Soumis le : Lundi 11 Juin 2007, 15:56:05

Dernière modification le : Lundi 18 Juin 2012, 14:11:17