{
  "id": "1601.00215",
  "version": "v1",
  "published": "2016-01-02T19:42:15.000Z",
  "updated": "2016-01-02T19:42:15.000Z",
  "title": "The Origin of UV-optical Variability in AGN and Test of Disc Models: XMM-Newton and ground based observations of NGC4395",
  "authors": [
    "Ian McHardy",
    "Sam Connolly",
    "Brad Peterson",
    "Allyson Bieryla",
    "Hum Chand",
    "Martin Elvis",
    "Dimitrios Emmanoulopoulos",
    "Emilio Falco",
    "Poshak Gandhi",
    "Shai Kaspi",
    "David Latham",
    "Paulina Lira",
    "Curtis McCully",
    "Hagai Netzer",
    "Makoto Uemura"
  ],
  "comment": "6 pages, 16 figures, accepted for publication in Astronomische Nachrichten",
  "categories": [
    "astro-ph.GA",
    "astro-ph.HE"
  ],
  "abstract": "The origin of short timescale (weeks/months) variability of AGN, whether due to intrinsic disc variations or reprocessing of X-ray emission by a surrounding accretion disc, has been a puzzle for many years. However recently a number of observational programmes, particularly of NGC5548 with Swift, have shown that the UV/optical variations lag behind the X-ray variations in a manner strongly supportive of X-ray reprocessing. Somewhat surprisingly the implied size of the accretion disc is ~3x greater than expected from a standard, smooth, Shakura-Sunyaev thin disc model. Although the difference may be explained by a clumpy accretion disc, it is not clear whether the difference will occur in all AGN or whether it may change as, eg, a function of black hole mass, accretion rate or disc temperature. Measurements of interband lags for most AGN require long timescale monitoring, which is hard to arrange. However for low mass (<1 million solar mass) AGN, the combination of XMM-Newton EPIC (X-rays) with the optical monitor in fast readout mode allows an X-ray/UV-optical lag to be measured within a single long observation. Here we summarise previous related observations and report on XMM-Newton observations of NGC4395 (mass ~100x lower and accretion rate ~20x lower than for NGC5548). We find that the UVW1 lags the X-rays by ~470s. Simultaneous observations at 6 different ground based observatories also allowed the g-band lag (~800s) to be measured. These observations are in agreement with X-ray reprocessing but initial analysis suggests that, for NGC4395, they do not differ markedly from the predictions of the standard thin disc model.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-01-02T19:42:15.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "observation",
      "uv-optical variability",
      "xmm-newton",
      "accretion disc",
      "shakura-sunyaev thin disc model"
    ],
    "publication": {
      "doi": "10.1002/asna.201612337"
    },
    "note": {
      "typesetting": "TeX",
      "pages": 6,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1412007
    }
  }
}