SCYON Abstract

Received on January 28 2010

Hard diffuse X-ray emission in the star-forming region ON2: discovery with XMM-Newton

AuthorsL. M. Oskinova, R. A. Gruendl, R. Ignace, Y.-H. Chu, W.-R. Hamann, and A. Feldmeier
AffiliationUniversity of Potsdam, University of Illinois, East Tennessee State University
Accepted byAstrophysical Journal
Contactlida@astro.physik.uni-potsdam.de
URLhttp://www.astro.physik.uni-potsdam.de/
Links Berkeley 87

Abstract

We obtained X-ray XMM-Newton observations of the open cluster Berkely 87 and the massive star-forming region (SFR) ON 2. In addition, archival infrared Spitzer Space Telescope observations were used. It is likely that the SFR ON 2 and Berkeley 87 are at the same distance, 1.23 kpc, and hence are associated. The XMM-Newton observations detected X-rays from massive stars in Berkeley 87 as well as diffuse emission from the SFR ON 2. The two patches of diffuse X-ray emission are encompassed in the shell-like H II region GAL 75.84+0.40 in the northern part of ON 2 and in the ON 2S region in the southern part of ON 2. The diffuse emission from GAL 75.84+0.40 suffers an absorption column equivalent to AV ~ 28 mag. Its spectrum can be fitted either with a thermal plasma model at T ≤ 30 MK or by an absorbed power-law model with γ ~ -2.6. The X-ray luminosity of GAL 75.84+0.40 is LX ~ 1 1032 erg/s. The diffuse emission from ON 2S is adjacent to the ultra-compact H II (UCHII) region Cygnus 2N, but does not coincide with it or with any other known UCHII region. It has a luminosity of LX ~ 6 1031 erg/s. The spectrum can be fitted with an absorbed power-law model with γ ~ -1.4. We adopt the view of Turner and Forbes (1982) that the SFR ON 2 is physically associated with the massive star cluster Berkeley 87 hosting the WO type star WR 142. We suggest that SFR ON 2 emits hard diffuse X-rays by a synchrotron mechanism, invoked by the co-existence of strongly shocked stellar winds and turbulent magnetic fields in the star-forming complex.