{
  "abstract": "We report the detection of hard X-ray pulsations from the M31 accreting non-ULX X-ray pulsar 3X J0042 (3XMM J004232.1+411314) using archival NuSTAR observations. The source has a spin period of ~3 s and an orbital period of ~4.15 hr, with coherent pulsations previously detected only in XMM-Newton observations. We reanalyse all five publicly available NuSTAR observations by correcting the photon arrival times for binary motion and optimizing the orbital epoch and projected semi-major axis. Coherent pulsations are detected in all five observations. The broad-band pulse profiles show similar morphology across the five observations spanning ~2.3 yr, with no significant long-term evolution. The pulse profile also shows energy dependence, with structured, non-sinusoidal profiles below ~20 keV and a less structured profile at higher energies. The pulse periods show an overall decrease over the ~2.3 yr NuSTAR baseline, continuing the long-term spin-up trend observed in the ~16 yr of XMM-Newton observations, but with a faster average spin-up rate of ~-1.1e-10 s/s compared to the earlier reported ~-6e-11 s/s. The short orbital period and inferred low-mass companion star shows it to be a low-mass X-ray binary containing a magnetized neutron star, with systems such as Her X-1, 3A 1822-371, and XMM J174457-2850.3 providing closer Galactic comparisons. This work represents the first detection of hard X-ray pulsations from a non-ULX extragalactic accreting pulsar.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.10699",
  "author_total": 2,
  "authors": [
    {
      "name": "Ketan Rikame"
    },
    {
      "name": "Biswajit Paul"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/2mvce650cdz5z.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.10699",
  "fulltext_url": null,
  "id": "2mvce650cdz5z",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.10699",
  "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": "W7212239542",
  "pdf_url": "https://arxiv.org/pdf/2609.10699",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-09",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/2mvce650cdz5z.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:26Z",
      "native_id": "2609.10699",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.10699"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Detection of hard X-ray pulsations in non-ULX X-ray pulsar 3X J0042 in M31",
  "title_text": "Detection of hard X-ray pulsations in non-ULX X-ray pulsar 3X J0042 in M31",
  "type": "preprint",
  "updated_at": "2026-10-30T12:20:26Z",
  "url": "https://research.draconitic.com/paper/2mvce650cdz5z",
  "venue": "arXiv",
  "versions": []
}