{
  "abstract": "In the hard state, X-ray emission from black hole X-ray binaries is attributed to Comptonization in the corona, a highly magnetized region near the black hole. Relativistic magnetic reconnection drives bulk motions that can upscatter soft photons and reproduce the spectral peak at $\\sim 100$ keV for parameters relevant to Cygnus X-1. However, the origin of the seed photons and of the MeV tail above the peak remains unclear. In 3D reconnection, so-called \"free\" particles escape the flux ropes and accelerate at the maximum rate set by the reconnection electric field. Their synchrotron emission extends to tens of MeV, which enables $γγ$ pair production with the Compton-upscattered photons. We present 3D particle-in-cell simulations of relativistic reconnection in pair plasma, in which particles cool by inverse Compton (IC) scattering below the synchrotron self-absorption threshold and by synchrotron radiation above it. Of the incoming magnetic power, $\\sim 40 \\%$ is converted to IC radiation and $\\gtrsim 10$-$20\\%$ to synchrotron. Using analytical estimates and radiative calculations for Cygnus X-1, we model how the radiation from reconnection-accelerated particles is reprocessed in the corona. Pair production attenuates the synchrotron emission above $\\sim 1$ MeV, and the escaping $γ$-rays form an MeV tail consistent with the observations, extending up to at least $\\sim 10$ MeV. Most of the absorbed power goes into secondary pairs, whose Thomson optical depth can reach order unity. Their synchrotron emission, peaking at $\\sim 0.1 \\, \\text{keV}$, can supply the seed photons for Comptonization. Our results support reconnection-based synchrotron self-Compton models of the hard-state emission in X-ray binaries.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2611.05307",
  "author_total": 5,
  "authors": [
    {
      "name": "Valeriia Rohoza"
    },
    {
      "name": "Maria Petropoulou"
    },
    {
      "name": "Hayk Hakobyan"
    },
    {
      "name": "Despina Karavola"
    },
    {
      "name": "Lorenzo Sironi"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/avj8ryc0dfhgc.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2611.05307",
  "fulltext_url": null,
  "id": "avj8ryc0dfhgc",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2611.05307",
  "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/2611.05307",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-03",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/avj8ryc0dfhgc.ris",
  "sources": [
    {
      "first_seen": "2026-11-04T15:21:25Z",
      "native_id": "2611.05307",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2611.05307"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Radiative relativistic reconnection powering the hard-state emission of X-ray binaries: synchrotron-driven pair loading, MeV tail, and seed photons",
  "title_text": "Radiative relativistic reconnection powering the hard-state emission of X-ray binaries: synchrotron-driven pair loading, MeV tail, and seed photons",
  "type": "preprint",
  "updated_at": "2026-11-06T18:21:01Z",
  "url": "https://research.draconitic.com/paper/avj8ryc0dfhgc",
  "venue": "arXiv",
  "versions": []
}