{
  "abstract": "Black hole X-ray binaries (BHXRBs) in the hard state show variable X-ray emission across a wide range of energies. Hard X-rays are thought to be produced through Compton-upscattering of seed photons from the accretion disc by the hot X-ray corona, leading to a spectral component roughly shaped like a power-law with a high-energy cut-off. A complete study of the coronal variability requires a full view of the spectrum, from the low-energy cut-off at the seed photon energy to the high energy cut-off, which may be related to the coronal temperature. We present a detailed spectral-timing study of strictly simultaneous observations by NICER and Insight-HXMT of the bright BHXRB MAXI~J1820+070, covering the 0.3-250 keV energy range. The high data quality allows us to study the lags and coherence across the full X-ray band. We find that at low Fourier frequencies ($\\lesssim0.02$ Hz), the soft X-ray flux below 1 keV and hard X-ray flux above 100 keV are anticorrelated, i.e. phase lags of $|π|$ rad. No anticorrelation is observed when comparing energy bands above 1 keV. We consider several explanations for the observed complex behaviour, such as a modulation of the coronal cut-off energy by the disc, power-law pivoting and a contribution from non-thermal electrons. Future, more detailed modelling efforts based on the observed effects may place new constraints on the dynamics of the X-ray emitting regions around accreting black holes.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: Mon Not R Astron Soc (2026)",
  "arxiv": "2609.27608",
  "author_total": 3,
  "authors": [
    {
      "name": "Niek Bollemeijer"
    },
    {
      "name": "Phil Uttley"
    },
    {
      "name": "Bei You"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/9qhrzr8ttb20v.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.27608",
  "fulltext_url": null,
  "id": "9qhrzr8ttb20v",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.27608",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.27608",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-23",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/9qhrzr8ttb20v.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:34:04Z",
      "native_id": "2609.27608",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.27608"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Broad-band spectral-timing: simultaneous NICER and HXMT observations reveal an anticorrelation between the softest and hardest X-ray fluxes in MAXI J1820+070",
  "title_text": "Broad-band spectral-timing: simultaneous NICER and HXMT observations reveal an anticorrelation between the softest and hardest X-ray fluxes in MAXI J1820+070",
  "type": "preprint",
  "updated_at": "2026-10-30T12:34:04Z",
  "url": "https://research.draconitic.com/paper/9qhrzr8ttb20v",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.1093/mnras/stag1829",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}