{
  "id": "1307.3246",
  "version": "v2",
  "published": "2013-07-11T20:00:01.000Z",
  "updated": "2013-09-04T17:49:03.000Z",
  "title": "The Spin of Supermassive Black Holes",
  "authors": [
    "Christopher S. Reynolds"
  ],
  "comment": "Invited article accepted for publication in the focus issue on astrophysical black holes in Classical and Quantum Gravity, guest editors: D. Merritt and L. Rezzolla. Minor revisions based on referee report and other feedback",
  "categories": [
    "astro-ph.HE",
    "gr-qc"
  ],
  "abstract": "Black hole spin is a quantity of great interest to both physicists and astrophysicists. We review the current status of spin measurements in supermassive black holes (SMBH). To date, every robust SMBH spin measurement uses X-ray reflection spectroscopy, so we focus almost exclusively on this technique as applied to moderately-luminous active galactic nuclei (AGN). After describing the foundations and uncertainties of the method, we summarize the current status of the field. At the time of writing, observations by XMM-Newton, Suzaku and NuSTAR have given robust spin constraints on 22 SMBHs. We find a significant number of rapidly-rotating SMBHs (with dimensionless spin parameters a>0.9) although, especially at the higher masses (M>4*10^7Msun), there are also some SMBHs with intermediate spin parameters. This may be giving us our first hint at a mass-dependent spin distribution which would, in turn, provide interesting constraints on models for SMBH growth. We also discuss the recent discovery of relativistic X-ray reverberation which we can use to \"echo map\" the innermost regions of the accretion disk. The ultimate development of these reverberation techniques, when applied to data from future high-throughput X-ray observatories such as LOFT, ATHENA+, and AXSIO, will permit the measurement of black hole spin by a characterization of strong-field Shapiro delays. We conclude with a brief discussion of other electromagnetic methods that have been attempted or are being developed to constrain SMBH spin.",
  "revisions": [
    {
      "version": "v2",
      "updated": "2013-09-04T17:49:03.000Z"
    }
  ],
  "analyses": {
    "subjects": [
      "98.62.Js"
    ],
    "keywords": [
      "supermassive black holes",
      "black hole spin",
      "robust smbh spin measurement",
      "current status",
      "intermediate spin parameters"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/0264-9381/30/24/244004",
      "journal": "Classical and Quantum Gravity",
      "year": 2013,
      "month": "Dec",
      "volume": 30,
      "number": 24,
      "pages": 244004
    },
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1242375,
      "adsabs": "2013CQGra..30x4004R"
    }
  }
}