Please use this identifier to cite or link to this item: http://hdl.handle.net/2440/49556
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Type: Journal article
Title: Detection of extended very-high-energy γ-ray emission towards the young stellar cluster Westerlund 2
Other Titles: Detection of extended very-high-energy gamma-ray emission towards the young stellar cluster Westerlund 2
Author: Aharonian, F.
Akhperjanian, A.
Bazer-Bachi, A.
Beilicke, M.
Benbow, W.
Berge, D.
Bernlohr, K.
Boisson, C.
Bolz, O.
Borrel, V.
Braun, I.
Brion, E.
Brown, A.
Buhler, R.
Busching, I.
Boutelier, T.
Carrigan, S.
Chadwick, P.
Chounet, L.
Coignet, G.
et al.
Citation: Astronomy and Astrophysics, 2007; 467(3):1075-1080
Publisher: E D P Sciences
Issue Date: 2007
ISSN: 0004-6361
1432-0746
Statement of
Responsibility: 
F. Aharonian...G. Rowell...et al.
Abstract: Aims. Results from γ-ray observations by the HESS telescope array in the direction of the young stellar cluster Westerlund 2 are presented. Methods. Stereoscopic imaging of Cherenkov light emission of γ-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. Results. The detection of a new γ-ray source is reported from HESS 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 9σ, and shows extension beyond a point-like object within the HESS point-spread function. The differential γ-ray spectrum of the emission region is measured over approximately two orders of magnitude in flux. Conclusions.The spatial coincidence between HESS J1023-575 and the young open cluster Westerlund 2, hosting e.g. the massive WR binary WR 20a, requires one to look into a variety of potential models to account for the observed very-high-energy (VHE) γ-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.
Keywords: ISM: individual objects: HESS J1023-575; ISM: individual objects: RCW 49 (NGC 3247, G284.3-0.3); stars: Wolf-Rayet; stars: individual: WR 20a; gamma rays: observations; ISM: HII regions
Rights: © ESO 2007
RMID: 0020074175
DOI: 10.1051/0004-6361:20066950
Appears in Collections:Chemistry and Physics publications

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