{
  "id": "2311.08697",
  "version": "v1",
  "published": "2023-11-15T04:54:28.000Z",
  "updated": "2023-11-15T04:54:28.000Z",
  "title": "First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass",
  "authors": [
    "The Event Horizon Telescope Collaboration"
  ],
  "comment": "65 pages, 35 figures, published in The Astrophysical Journal Letters on May 12, 2022. See the published paper for the full authors list",
  "journal": "The Astrophysical Journal Letters, Volume 930, Number 2, id L15, 52pp., 2022 May 12",
  "doi": "10.3847/2041-8213/ac6736",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "In this paper we quantify the temporal variability and image morphology of the horizon-scale emission from Sgr A*, as observed by the EHT in 2017 April at a wavelength of 1.3 mm. We find that the Sgr A* data exhibit variability that exceeds what can be explained by the uncertainties in the data or by the effects of interstellar scattering. The magnitude of this variability can be a substantial fraction of the correlated flux density, reaching $\\sim$100\\% on some baselines. Through an exploration of simple geometric source models, we demonstrate that ring-like morphologies provide better fits to the Sgr A* data than do other morphologies with comparable complexity. We develop two strategies for fitting static geometric ring models to the time-variable Sgr A* data; one strategy fits models to short segments of data over which the source is static and averages these independent fits, while the other fits models to the full dataset using a parametric model for the structural variability power spectrum around the average source structure. Both geometric modeling and image-domain feature extraction techniques determine the ring diameter to be $51.8 \\pm 2.3$ $\\mu$as (68\\% credible intervals), with the ring thickness constrained to have an FWHM between $\\sim$30\\% and 50\\% of the ring diameter. To bring the diameter measurements to a common physical scale, we calibrate them using synthetic data generated from GRMHD simulations. This calibration constrains the angular size of the gravitational radius to be $4.8_{-0.7}^{+1.4}$ \\mathrm{\\mu as}, which we combine with an independent distance measurement from maser parallaxes to determine the mass of Sgr A* to be $4.0_{-0.6}^{+1.1} \\times 10^6$ M$_{\\odot}$.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-11-15T04:54:28.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "event horizon telescope results",
      "black hole mass",
      "variability",
      "first sagittarius",
      "morphology"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 65,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}