{
  "id": "1704.06110",
  "version": "v1",
  "published": "2017-04-20T12:35:24.000Z",
  "updated": "2017-04-20T12:35:24.000Z",
  "title": "Extended Gamma-ray Emission from the G25.0+0.0 Region: A Star Forming Region Powered by the Newly Found OB Association?",
  "authors": [
    "Junichiro Katsuta",
    "Yasunobu Uchiyama",
    "Stefan Funk"
  ],
  "comment": "31 pages, 23 figures, accepted for publication in ApJ",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We report a study of extended $\\gamma$-ray emission with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope, which is likely to be the second case of a $\\gamma$-ray detection from a star-forming region (SFR) in our Galaxy. The LAT source is located in the G25 region, $1.7^{\\circ} \\times 2.1^{\\circ}$ around $(l, b) = (25.0^{\\circ}, 0.0^{\\circ})$. The $\\gamma$-ray emission is found to be composed of two extended sources and one point-like source. The extended sources have a similar sizes of about $1.4^{\\circ} \\times 0.6^{\\circ}$. An $\\sim 0.4^{\\circ}$ diameter sub-region of one has a photon index of $\\Gamma = 1.53 \\pm 0.15$; 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 $\\Gamma = 2.1 \\pm 0.2$ without significant spectral curvature. Given their spatial and spectral properties, they have no clear associations with sources at other wavelengths. Their $\\gamma$-ray properties are similar to those of the Cygnus cocoon SFR, the only firmly established $\\gamma$-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 $\\gamma$-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 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 $\\gamma$-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.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-04-20T12:35:24.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "extended gamma-ray emission",
      "star forming region",
      "young massive ob association/cluster",
      "cygnus cocoon",
      "emitting regions appear"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 31,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}