{
  "abstract": "Her X-1 is an eclipsing X-ray binary system consisting of an accreting neutron star and an optical component HZ Her. In addition to the 1.24-s X-ray pulsations and the 1.7-d orbital period, the system also shows a 35-day X-ray variability related to the precessional motion of a tilted and twisted accretion disk around the neutron star. The long-term persistence of the 35-day X-ray variability suggests the presence of a stable clock mechanism, most likely free precession of the magnetized neutron star. We have studied the long-term behavior of the 35-day cycle of Her X-1 using all available CGRO/BATSE, RXTE/ASM, Swift/BAT, Fermi/GBM, MAXI data and archival turn-on moments of the 35-day cycle spanning more than 50 years. We have used a sliding-window averaged X-ray phase light curve and the classical O-C (observed minus calculated) diagram for individual 35-day turn-ons to inspect the long-term trends of the O-C diagram. The O-C diagram demonstrates two similar parabolic trends separated by an anomalous low state (ALS) of the source suggesting a secular decrease in the 35-d precession period with $\\dot P_\\text{35} =(-1.3\\pm0.2)\\times10^{-5} \\,\\mathrm{~s\\,s}^{-1}$ and $\\dot P_\\text{35} =(-4.7\\pm0.1)\\times10^{-5} \\,\\mathrm{~s\\,s}^{-1}$ before and after the ALS, respectively. We conclude that the decay of the 35-day period as inferred from the O-C analysis can be interpreted in terms of the direct relationship between the change of the precessional period of the accretion disk to the long-term decrease of the period of the free precessional neutron star - due to continued accumulation of accreted matter.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.41734",
  "author_total": 6,
  "authors": [
    {
      "name": "Vladislav Revnivtsev"
    },
    {
      "name": "Konstantin Postnov"
    },
    {
      "name": "Ruediger Staubert"
    },
    {
      "name": "Sergey Antipin"
    },
    {
      "name": "Sergey Molkov"
    },
    {
      "name": "Nikolai Shakura"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/38ch13881g8b6.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.41734",
  "fulltext_url": null,
  "id": "38ch13881g8b6",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.41734",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2610.41734",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-30",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/38ch13881g8b6.ris",
  "sources": [
    {
      "first_seen": "2026-11-02T12:21:15Z",
      "native_id": "2610.41734",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.41734"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Long-term variability of the 35-day cycle in Her X-1",
  "title_text": "Long-term variability of the 35-day cycle in Her X-1",
  "type": "preprint",
  "updated_at": "2026-11-04T15:20:51Z",
  "url": "https://research.draconitic.com/paper/38ch13881g8b6",
  "venue": "arXiv",
  "versions": []
}