{
  "id": "2409.08451",
  "version": "v1",
  "published": "2024-09-13T00:53:33.000Z",
  "updated": "2024-09-13T00:53:33.000Z",
  "title": "The Puzzling Superorbital Period Variation of the Low-mass X-ray Binary 4U 1820-30",
  "authors": [
    "Yi Chou",
    "Jun-Lei Wu",
    "Bo-Chun Chen",
    "Wei-Yun Chang"
  ],
  "comment": "15 pages, 8 figures, submitted to ApJ",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "Because of the previously observed stability of the 171-day period, the superorbital modulation of the low-mass X-ray binary 4U 1820-30 was considered a consequence of a third star orbiting around the binary. This study aims to further verify this triple model by testing the stability of superorbital period using the light curves collected by X-ray sky monitoring/scanning telescopes from 1987 to 2023. Both power spectral and phase analysis results indicate a significant change in the superorbital period from 171 days to 167 days over this 36-year span. The evolution of the superorbital phase suggests that the superorbital period may have experienced an abrupt change between late 2000 and early 2023 or changed gradually with a period derivative of $\\dot P_{sup}=(-3.58 \\pm 0.72) \\times 10^{-4}$ day/day. We conclude that the superorbital period of 4U 1820-30 was not as stable as anticipated by the triple model, which strongly challenges this hypothesis. Instead, we propose an irradiation-induced mass transfer instability scenario to explain the superorbital modulation of 4U 1820-30.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2024-09-13T00:53:33.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "low-mass x-ray binary 4u",
      "puzzling superorbital period variation",
      "mass transfer instability scenario",
      "triple model",
      "superorbital modulation"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 15,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}