{
  "id": "1005.0803",
  "version": "v1",
  "published": "2010-05-05T18:10:33.000Z",
  "updated": "2010-05-05T18:10:33.000Z",
  "title": "Gamma-ray absorption and the origin of the gamma-ray flare in Cygnus X-1",
  "authors": [
    "Gustavo E. Romero",
    "Maria Victoria del Valle",
    "Mariana Orellana"
  ],
  "comment": "9 pages, 7 figures",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "The high-mass microquasar Cygnus X-1, the best-established candidate for a stellar-mass black hole in the Galaxy, has been detected in a flaring state at very high energies (VHE), E > 200 GeV, by the Atmospheric Cherenkov Telescope MAGIC. The flare occurred at orbital phase 0.91, where phase 1 is the configuration with the black hole behind the companion high-mass star, when the absorption of gamma-ray photons by photon-photon annihilation with the stellar field is expected to be highest. We aim to set up a model for the high-energy emission and absorption in Cyg X-1 that can explain the nature of the observed gamma-ray flare. We study the gamma-ray opacity due to pair creation along the whole orbit, and for different locations of the emitter. Then we consider a possible mechanism for the production of the VHE emission. We present detailed calculations of the gamma-ray opacity and infer from these calculations the distance from the black hole where the emitting region was located. We suggest that the flare was the result of a jet-clump interaction where the decay products of inelastic proton-proton collisions dominate the VHE outcome. We are able to reproduce the spectrum of Cyg X-1 during the observed flare under reasonable assumptions. The flare may be the first event of jet-cloud interaction ever detected at such high energies.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2010-05-05T18:10:33.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "gamma-ray flare",
      "gamma-ray absorption",
      "inelastic proton-proton collisions dominate",
      "high energies",
      "atmospheric cherenkov telescope magic"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1051/0004-6361/200913938",
      "journal": "Astronomy and Astrophysics",
      "year": 2010,
      "month": "Jul",
      "volume": 518
    },
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 854010,
      "adsabs": "2010A&A...518A..12R"
    }
  }
}