{
  "id": "1704.00474",
  "version": "v1",
  "published": "2017-04-03T08:46:34.000Z",
  "updated": "2017-04-03T08:46:34.000Z",
  "title": "Simultaneous Optical/X-ray study of GS 1354-64 (=BW Cir) during hard outburst: evidence for optical cyclo-synchrotron emission from the hot accretion flow",
  "authors": [
    "Mayukh Pahari",
    "Poshak Gandhi",
    "Philip A. Charles",
    "Marissa M. Kotze",
    "Diego Altamirano",
    "Ranjeev Misra"
  ],
  "comment": "15 pages, 11 figures, accepted for publication in MNRAS",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We present results from simultaneous optical (SALT) and X-ray (Swift and INTEGRAL) observations of GS 1354-64/BW Cir during the 2015 hard state outburst. During the rising phase, optical/X-ray time series show a strong anti-correlation with X-ray photons lagging optical. Optical and X-ray power spectra show quasi-periodic oscillations at a frequency of ~18 mHz with a confidence level of at least 99%. Simultaneous fitting of Swift/XRT and INTEGRAL spectra in the range 0.5-1000 keV shows non-thermal, power-law dominated (> 90%) spectra with a hard power-law index of 1.48 +/- 0.03, inner disc temperature of 0.12 +/- 0.01 keV and inner disc radius of ~3000 km. All evidence is consistent with cyclo-synchrotron radiation in a non-thermal, hot electron cloud extending to ~100 Schwarzschild radii being a major physical process for the origin of optical photons. At outburst peak about one month later, when the X-ray flux rises and the optical drops, the apparent features in the optical/X-ray correlation vanish and the optical auto correlation widens. Although ~0.19 Hz QPO is observed from the X-ray power spectra, the optical variability is dominated by the broadband noise, and the inner disc temperature increases. These results support a change in the dominant optical emission source between outburst rise and peak, consistent with a weakening of hot flow as the disc moves in.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-04-03T08:46:34.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "hot accretion flow",
      "simultaneous optical/x-ray study",
      "optical cyclo-synchrotron emission",
      "hard outburst",
      "x-ray power spectra"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 15,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}