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

Abstract

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.

7 pages, 5 figures, accepted for publication in A&A

References in corpus (21)

• Observations of the Crab Nebula with H.E.S.S
• The H.E.S.S. survey of the Inner Galaxy in very high-energy gamma-rays
• A new population of very high energy gamma-ray sources in the Milky Way
• A census of the Wolf-Rayet content in Westerlund 1 from near-infrared imaging and spectroscopy
• Gamma-ray absorption in massive X-ray binaries
• WR 20a is an Eclipsing Binary: Accurate Determination of Parameters for an Extremely Massive Wolf-Rayet System
• Radio, X-ray, and gamma-ray Emission Models of the Colliding Winds Binary WR 140
• Non-thermal high-energy emission from colliding winds of massive stars
• The Southern Galactic Plane Survey: The Test Region
• Gamma-ray emission from Wolf-Rayet binaries
• WR20a: a massive cornerstone binary system comprising two extreme early-type stars
• Diffuse, Non-Thermal X-ray Emission from the Galactic Star Cluster Westerlund 1
• Early-type stars in the core of the young open cluster Westerlund2
• The Cluster Wind from Local Massive Star Clusters
• A GLIMPSE of Star Formation in the Giant H II Region RCW 49
• High-energy gamma-rays from stellar associations
• MSX Mid infrared imaging of massive star birth environments. II: Giant HII regions
• WR146 - observing the OB-type companion
• The dominant X-ray wind in massive star binaries
• Hadronic processes within collective stellar winds
• GeV gamma-rays and TeV neutrinos from very massive compact binary systems: The case of WR 20a

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