{
  "id": "1207.7267",
  "version": "v2",
  "published": "2012-07-31T14:41:25.000Z",
  "updated": "2016-03-14T17:25:59.000Z",
  "title": "Gamma-ray emission from globular clusters",
  "authors": [
    "P. H. Thomas Tam",
    "C. Y. Hui",
    "Albert K H. Kong"
  ],
  "comment": "11 pages, 7 figures, 2 tables, J. Astron. Space Sci., in press",
  "journal": "J. Astron. Space Sci. (2016) Vol. 33 issue 1 page 1",
  "categories": [
    "astro-ph.HE",
    "astro-ph.GA"
  ],
  "abstract": "Over the last few years, the data obtained using the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope has provided new insights on high-energy processes in globular clusters, particularly those involving compact objects such as Millisecond Pulsars (MSPs). Gamma-ray emission in the 100 MeV to 10 GeV range has been detected from more than a dozen globular clusters in our galaxy, including 47 Tucanae and Terzan 5. Based on a sample of known gamma-ray globular clusters, the empirical relations between gamma-ray luminosity and properties of globular clusters such as their stellar encounter rate, metallicity, and possible optical and infrared photon energy densities, have been derived. The measured gamma-ray spectra are generally described by a power law with a cut-off at a few gigaelectronvolts. Together with the detection of pulsed gamma-rays from two MSPs in two different globular clusters, such spectral signature lends support to the hypothesis that gamma-rays from globular clusters represent collective curvature emission from magnetospheres of MSPs in the clusters. Alternative models, involving Inverse-Compton (IC) emission of relativistic electrons that are accelerated close to MSPs or pulsar wind nebula shocks, have also been suggested. Observations at >100 GeV by using Fermi/LAT and atmospheric Cherenkov telescopes such as H.E.S.S.-II, MAGIC-II, VERITAS, and CTA will help to settle some questions unanswered by current data.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2012-07-31T14:41:25.000Z",
      "abstract": "Over the last few years, the fruitful data provided by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope has revolutionized our understanding of high-energy processes in globular clusters, particularly those involving compact objects like millisecond pulsars (MSPs). Gamma-ray emission between 100 MeV to 10 GeV has been detected from more than a dozen globular clusters in our Galaxy, most notably 47 Tucanae and Terzan 5. Based on a sample of known gamma-ray globular clusters, empirical relations between the gamma-ray luminosity and properties of globular clusters such as stellar encounter rate, metallicity, as well as optical and infrared photon energy density in the cluster, have been derived. The gamma-ray spectra are generally described by a power law with a cut-off at a few GeV. Together with the detection of pulsed gamma-rays from a millisecond pulsar in a globular cluster, such spectral signature gives support that gamma-rays from globular clusters are collective curvature emission from magnetospheres of MSPs within the cluster. Alternative models in which the inverse-Compton emission of relativistic electrons accelerated close to MSPs or the pulsar wind nebula shocks have also been suggested. Observations at >10 GeV by Fermi/LAT and atmospheric Cherenkov telescopes like H.E.S.S.-II, MAGIC-II, VERITAS, and CTA will help to settle some questions unanswered by current data. We also discuss TeV observations of globular clusters, as well as observational prospects of gravitational waves from double neutron stars in globular clusters.",
      "comment": "14 pages, 5 figures, 2 tables, submitted to New Astronomy Reviews",
      "journal": null,
      "doi": null,
      "authors": [
        "P. H. Thomas Tam",
        "Albert K. H. Kong",
        "C. Y. Hui"
      ]
    },
    {
      "version": "v2",
      "updated": "2016-03-14T17:25:59.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "gamma-ray emission",
      "large area telescope aboard",
      "fermi gamma-ray space telescope",
      "millisecond pulsar",
      "pulsar wind nebula shocks"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 11,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1124309,
      "adsabs": "2012arXiv1207.7267T"
    }
  }
}