Astrophys. J., 839, 129-129 (2017/April-3)
Extended Gamma-ray emission from the G25.0+0.0 region: a star-forming region powered by the newly found OB association?
KATSUTA J., UCHIYAMA Y. and FUNK S.
Abstract (from CDS):
We report a study of extended γ-ray emission with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope, which is likely to be the second case of a γ-ray detection from a star-forming region (SFR) in our Galaxy. The LAT source is located in the G25 region, 1.°7 x 2.°1 around (l, b) = (25.°0, 0.°0). The γ-ray emission is found to be composed of two extended sources and one pointlike source. The extended sources have similar sizes of about 1.°4 x 0.°6. An ∼0.°4 diameter subregion of one has a photon index of Γ = 1.53 ± 0.15, and is spatially coincident with HESS J1837-069, likely a pulsar wind nebula. The other parts of the extended sources have a photon index of Γ = 2.1 ± 0.2 without significant spectral curvature. Given their spatial and spectral properties, they have no clear associations with sources at other wavelengths. Their γ-ray properties are similar to those of the Cygnus cocoon SFR, the only firmly established γ-ray detection of an SFR in the Galaxy. Indeed, we find bubble-like structures of atomic and molecular gas in G25, which may be created by a putative OB association/cluster. The γ-ray emitting regions appear confined in the bubble-like structure; similar properties are also found in the Cygnus cocoon. In addition, using observations with the XMM-Newton, we find a candidate young massive OB association/cluster G25.18+0.26 in the G25 region. We propose that the extended γ-ray emission in G25 is associated with an SFR driven by G25.18+0.26. Based on this scenario, we discuss possible acceleration processes in the SFR and compare them with the Cygnus cocoon.
© 2017. The American Astronomical Society. All rights reserved.
acceleration of particles - cosmic rays - gamma rays: ISM - ISM: bubbles - open clusters and associations: general - X-rays: stars - X-rays: stars
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