{
  "id": "2210.02879",
  "version": "v1",
  "published": "2022-10-06T13:01:23.000Z",
  "updated": "2022-10-06T13:01:23.000Z",
  "title": "Observational Constrains on Direct Electron Heating in Hot Accretion Flows from Sgr A* and M87*",
  "authors": [
    "Fu-Guo Xie",
    "Ramesh Narayan",
    "Feng Yuan"
  ],
  "comment": "8 pages, 2 figures. Submitted to AAS journal. Comments welcomed",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "An important parameter in the theory of hot accretion flows around black holes is $\\delta$, which describes the fraction of ``viscously'' dissipated energy in the accretion flow that directly heats the electrons. The radiative efficiency of a hot accretion flow is determined by its value if other parameters, such as the accretion rate, are determined. Unfortunately, the value of $\\delta$ is hard to determine from first principles. The recent Event Horizon Telescope Collaboration (EHTC) results on M87* and Sgr A* provide us with a different way of constraining $\\delta$. By combining the mass accretion rates in M87* and Sgr A* estimated by the EHTC with the measured bolometric luminosities of the two sources, we derive good constraints on the radiative efficiencies of the respective accretion flows. In parallel, we use a theoretical model of hot magnetically arrested disks (MAD) to calculate the expected radiative efficiency as a function of $\\delta$ (and accretion rate). By comparing the EHTC-derived radiative efficiencies with the theoretical MAD model, we find that Sgr A* requires $\\delta > 0.3$, with the most likely value being $\\delta \\sim 0.5$. A similar comparison in the case of M87* gives inconclusive results, because there is still a large uncertainty in the accretion rate in this source.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2022-10-06T13:01:23.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "hot accretion flow",
      "direct electron heating",
      "observational constrains",
      "radiative efficiency",
      "event horizon telescope collaboration"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 8,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}