{
  "id": "1001.0870",
  "version": "v1",
  "published": "2010-01-06T11:40:46.000Z",
  "updated": "2010-01-06T11:40:46.000Z",
  "title": "In-depth studies of the NGC 253 ULXs with XMM-Newton: remarkable variability in ULX1, and evidence for extended coronae",
  "authors": [
    "R. Barnard"
  ],
  "comment": "Accepted for publication in MNRAS. 7 pages, 5 figures",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We examined the variability of three ultra-luminous X-ray sources (ULXs) in the 2003, 110 ks XMM-Newton observation of NGC253. Remarkably, we discovered ULX1 to be three times more variable than ULX2 in the 0.3--10 keV band, even though ULX2 is brighter. Indeed, ULX1 exhibits a power density spectrum that is consistent with the canonical high state or very high/steep power law state, but not the canonical low state. The 0.3--10 keV emission of ULX1 is predominantly non-thermal, and may be related to the very high state. We also fitted the ULX spectra with disc blackbody, slim disc and convolution Comptonization (SIMPL x DISKBB) models. The brightest ULX spectra are usually described by a two emission components (disc blackbody + Comptonized component); however, the SIMPL model results in a single emission component, and may help determine whether the well known soft excess is a feature of ULX spectra or an artifact of the two-component model. The SIMPL models were rejected for ULX3 (and also for the black hole + Wolf-Rayet binary IC10 X-1); hence, we infer that the observed soft-excesses are genuine features of ULX emission spectra. We use an extended corona scenario to explain the soft excess seen in all the highest quality ULX spectra, and provide a mechanism for stellar mass black holes to exhibit super-Eddington luminosities while remaining locally sub-Eddington.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2010-01-06T11:40:46.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "extended corona",
      "in-depth studies",
      "xmm-newton",
      "variability",
      "high/steep power law state"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1111/j.1365-2966.2010.16291.x",
      "journal": "Monthly Notices of the Royal Astronomical Society",
      "year": 2010,
      "month": "May",
      "volume": 404,
      "number": 1,
      "pages": 42
    },
    "note": {
      "typesetting": "TeX",
      "pages": 7,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 841905,
      "adsabs": "2010MNRAS.404...42B"
    }
  }
}