{
  "id": "1510.01414",
  "version": "v1",
  "published": "2015-10-06T02:08:44.000Z",
  "updated": "2015-10-06T02:08:44.000Z",
  "title": "Temporal evolution of long-timescale periodicities in ULX NGC 5408 X-1",
  "authors": [
    "Tao An",
    "Xiang-Long Lu",
    "Jun-Yi Wang"
  ],
  "comment": "7 pages, 6 figures, accepted for publication in Astronomy and Astrophysics on 21/09/2015",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "Context. NGC 5408 X-1 is one of the few ultraluminous X-ray sources with an extensive monitoring program in X-rays (a temporal baseline of 4.2 yr), making it one of the most suitable candidates to study the long-timescale quasi-periodic oscillations (QPOs). Aims. Previous timing analysis of the Swift data of NGC 5408 X-1 led to detection of multiple periodicities ranging from 2.6 d to 230 d. In this paper, we focus on the statistical significance and the temporal evolution of these periodicities. Methods. A time-series analysis technique in the time-frequency domain, the weighted wavelet Z-transform (WWZ), was employed to identify the periodicities and trace their variations with time. Results. Three periodic components were detected from the WWZ periodogram, corresponding to periods of 2.65$\\pm$0.01 d, 115.4$\\pm$14.4 d and 189.1$\\pm$15.2 d. All three have statistical significance higher than 99.74%. The 2.65-d periodicity is quite stable in the majority of the light curve. The 115-d periodicity is the most prominent but appears variable. The 189-d periodicity is persistent across the whole time coverage. It shows a steadily decreasing trend from the beginning (193 d period) to the end (181 d period). Conclusions. The long-timescale periodicities in NGC 5408 X-1 are most likely of super-orbital origin, and are probably associated with the precession of a warped accretion disc. The disc may have been broken into two distinct planes with different precessing periods, i.e. the 189-d and 115-d periodicities corresponding to the outer and inner disc, respectively.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-10-06T02:08:44.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "periodicity",
      "long-timescale periodicities",
      "temporal evolution",
      "ulx ngc",
      "long-timescale quasi-periodic oscillations"
    ],
    "publication": {
      "doi": "10.1051/0004-6361/201526182"
    },
    "note": {
      "typesetting": "TeX",
      "pages": 7,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1396283
    }
  }
}