{
  "abstract": "Hercules X-1 and Centaurus X-3 are the first ever detected - and as such identified - binary X-ray pulsars. Here we concern ourselves with the 35-day flux modulation of Her X-1, immediately found at its discovery, together with the binary period of 1.7 days and the pulsation with 1.24 s. The 35-day flux modulation shows two flux maxima, the so-called Main-On and the Short-On (with reduced flux). As noticed early on, the period, or the length of the cycle, is variable. The system constitutes an irregular clock, with a more or less stable mean period of near 34.85 d. We consider the repeated rapid increases of the flux from the off-state to the Main-On (the socalled Turn-Ons) as the best timing marker to study this clock. Here we present a complete list of Turn-On times over 55 years, from the discovery of Her X-1 to today (2026), based on historic work from the literature and on observational data provided by five monitoring instruments. We identify to following basic features of the irregular 35-day clock: The Turn-Ons show preference to occur at orbital phases 0.25 and 0.75. The duration of the 35-day cycle clusters around three discrete values - 20.0, 20.5 and 21.0 orbital cycles with a dominant peak at 20.5 Porb (57%). The long-term trend in the 35-day period duration is seen in the O-C (Observed minus Calculated) diagram. There are two sections, separated by the long Anomalous Low of 1999/200 (AL3), which can be modeled by parabolic functions with a smooth evolution of the 35-day period. A medium-term variation is observed in the form of Anomalous Lows, an essential shut-off (at least of soft) X-rays. We find an apparent underlying period of 5.4 yr. There are short-term (hundreds of days) variations (in part quasi-periodic) overlaid to the long-term trend. Straight ups and downs in the O-C diagram, demonstrating rather rapid 35 day period changes.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.36987",
  "author_total": 4,
  "authors": [
    {
      "name": "Ruediger Staubert"
    },
    {
      "name": "Konstantin Postnov"
    },
    {
      "name": "Vladislav Revnivtsev"
    },
    {
      "name": "Lorenzo Ducci"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/52scz0anbry9a.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.36987",
  "fulltext_url": null,
  "id": "52scz0anbry9a",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.36987",
  "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",
      "3103|Astrophysical Phenomena and Observations"
    ]
  ],
  "openalex": "W7224131546",
  "pdf_url": "https://arxiv.org/pdf/2610.36987",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-27",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/52scz0anbry9a.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:35:50Z",
      "native_id": "2610.36987",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.36987"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "History of Turn-Ons - the irregular 35-day clock - of Hercules X-1",
  "title_text": "History of Turn-Ons - the irregular 35-day clock - of Hercules X-1",
  "type": "preprint",
  "updated_at": "2026-10-30T12:35:50Z",
  "url": "https://research.draconitic.com/paper/52scz0anbry9a",
  "venue": "arXiv",
  "versions": []
}