{
  "id": "1601.02740",
  "version": "v1",
  "published": "2016-01-12T06:10:29.000Z",
  "updated": "2016-01-12T06:10:29.000Z",
  "title": "MAXI observations of long-term variations of Cygnus X-1 in the low/hard and the high/soft states",
  "authors": [
    "Juri Sugimoto",
    "Tatehiro Mihara",
    "Shunji Kitamoto",
    "Masaru Matsuoka",
    "Mutsumi Sugizaki",
    "Hitoshi Negoro",
    "Satoshi Nakahira",
    "Kazuo Makishima"
  ],
  "comment": "17 pages, 15 figures, accepted for publication in PASJ",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "Long-term X-ray variability of the black hole binary, Cygnus X-1, was studied with five years of MAXI data from 2009 to 2014, which include substantial periods of the high/soft state, as well as the low/hard state. In each state, Normalized Power Spectrum densities (NPSDs) were calculated in three energy bands of 2-4 keV, 4-10 keV and 10-20 keV. The NPSDs in a frequency from 1e-7 Hz to 1e-4 Hz are all approximated by a power-law function with an index -1.35 ~ -1.29. The fractional RMS variation ($\\eta$), calculated in the above frequency range, was found to show the following three properties; (1) $\\eta$ slightly decreases with energy in the low/hard state; (2) $\\eta$ increases towards higher energies in the high/soft state; and (3) in the 10-20 keV band, $\\eta$ is 3 times higher in the high/soft state than in the low/hard state. These properties were confirmed through studies of intensity-correlated changes of the MAXI spectra. Of these three findings, the first one is consistent with that seen in the short-term variability during the LHS. The latter two can be understood as a result of high variability of the hard-tail component seen in the high/soft state with the above very low frequency range, although the origin of the variability remains inconclusive.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-01-12T06:10:29.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "high/soft state",
      "long-term variations",
      "maxi observations",
      "low/hard state",
      "low frequency range"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 17,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1414913
    }
  }
}