{
  "id": "1801.06164",
  "version": "v1",
  "published": "2018-01-18T18:32:52.000Z",
  "updated": "2018-01-18T18:32:52.000Z",
  "title": "Evidence for a decreasing X-ray afterglow emission of GW170817A and GRB 170817A in XMM-Newton",
  "authors": [
    "P. D'Avanzo",
    "S. Campana",
    "G. Ghisellini",
    "A. Melandri",
    "M. G. Bernardini",
    "S. Covino",
    "V. D'Elia",
    "L. Nava",
    "R. Salvaterra",
    "G. Tagliaferri",
    "S. D. Vergani"
  ],
  "comment": "Letter submitted to Astronomy & Astrophysics. Other authors will be added to the present author list as soon as they have permission from the respective collaborations",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We report our observation of the short GRB 170817A, associated to the binary neutron star merger event GW 170817, perfomed in the X-ray band with XMM-Newton 135 d after the event (on the 29th December 2017). We find that the X-ray light curve started to decrease with respect to the previous steadily brightening trend. This is also supported by a nearly simultaneous optical Hubble Space Telescope observation. Since the optical-to-X-ray spectral slope did not change with respect to previous observations, we exclude that the decrease in flux is due to the passage of the cooling frequency: its origin must be geometric or dynamical. We interpret all the existing afterglow data with two models: i) a structured jet and ii) a jet-less isotropic fireball with some stratification in its radial velocity structure. Both models fit the data and predict that the radio flux must decrease simultaneously with the optical and the X-ray one, making hard to distinguish between them at the present stage. Polarimetric measures and the rate of short GRB-GW association in future LIGO/Virgo runs will be key to disentangle these two geometrically different scenarios.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-01-18T18:32:52.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "decreasing x-ray afterglow emission",
      "grb 170817a",
      "star merger event gw",
      "hubble space telescope observation",
      "optical hubble space telescope"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}