{
  "id": "1506.03083",
  "version": "v1",
  "published": "2015-06-09T20:01:10.000Z",
  "updated": "2015-06-09T20:01:10.000Z",
  "title": "Infrared identification of hard X-ray sources in the Galaxy",
  "authors": [
    "A. Nebot Gómez-Morán",
    "C. Motch",
    "F. -X. Pineau",
    "F. J. Carrera",
    "M. W. Pakull",
    "F. Riddick"
  ],
  "comment": "19 pages, 13 figures, 7 tables (accepted for publication, MNRAS)",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "The nature of the low- to intermediate-luminosity (Lx$\\,\\sim 10^{32-34}$ erg s$^{-1}$) source population revealed in hard band (2-10 keV) X-ray surveys of the Galactic Plane is poorly understood. To overcome such problem we cross-correlated the XMM-Newton 3XMM-DR4 survey with the infrared 2MASS and GLIMPSE catalogues. We identified reliable X-ray-infrared associations for 690 sources. We selected 173 sources having hard X-ray spectra, typical of hard X-ray high-mass stars (kT$\\,>\\,5\\,$keV), and 517 sources having soft X-ray spectra, typical of active coronae. About $18\\,\\%$ of the soft sources are classified in the literature: $\\sim\\,91\\%$ as stars, with a minor fraction of WR stars. Roughly $15\\,\\%$ of the hard sources are classified in the literature: $\\sim\\,68\\%$ as high-mass X-ray stars single or in binary systems (WR, Be and HMXBs), with a small fraction of G and B stars. We carried out infrared spectroscopic pilot observations at the William Herschel Telescope for five hard X-ray sources. Three of them are high-mass stars with spectral types WN7-8h, Ofpe/WN9 and Be, and Lx$\\sim\\,10^{32}-10^{33}$erg s$^{-1}$. One source is a colliding-wind binary, while another source is a colliding-wind binary or a supergiant fast X-ray transient in quiescence. The Be star is a likely $\\gamma$-Cas system. The nature of the other two X-ray sources is uncertain. The distribution of hard X-ray sources in the parameter space made of X-ray hardness ratio, infrared colours and X-ray-to-infrared flux ratio suggests that many of the unidentified sources are new $\\gamma$-Cas analogues, WRs and low Lx HMXBs. However, the nature of the X-ray population with Ks $\\geq$ 11 and average X-ray-to-infrared flux ratio remains unconstrained.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-06-09T20:01:10.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "hard x-ray sources",
      "infrared identification",
      "supergiant fast x-ray transient",
      "average x-ray-to-infrared flux ratio remains",
      "colliding-wind binary"
    ],
    "publication": {
      "doi": "10.1093/mnras/stv1020"
    },
    "note": {
      "typesetting": "TeX",
      "pages": 19,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1375460
    }
  }
}