{
  "id": "2001.07446",
  "version": "v1",
  "published": "2020-01-21T11:14:20.000Z",
  "updated": "2020-01-21T11:14:20.000Z",
  "title": "Extreme variability in an active galactic nucleus: Gaia16aax",
  "authors": [
    "G. Cannizzaro",
    "M. Fraser",
    "P. G. Jonker",
    "J. E. Pringle",
    "S. Mattila",
    "P. C. Hewett",
    "T. Wevers",
    "E. Kankare",
    "Z. Kostrzewa-Rutkowska",
    "Ł. Wyrzykowski",
    "F. Onori",
    "J. Harmanen",
    "K. E. S. Ford",
    "B. McKernan",
    "C. J. Nixon"
  ],
  "comment": "21 pages, 17 figure - accepted for publication in MNRAS main journal",
  "categories": [
    "astro-ph.HE",
    "astro-ph.GA"
  ],
  "abstract": "We present the results of a multi-wavelength follow up campaign for the luminous nuclear transient Gaia16aax, which was first identified in January 2016. The transient is spatially consistent with the nucleus of an active galaxy at z=0.25, hosting a black hole of mass $\\rm \\sim6\\times10^8M_\\odot$. The nucleus brightened by more than 1 magnitude in the Gaia G-band over a timescale of less than one year, before fading back to its pre-outburst state over the following three years. The optical spectra of the source show broad Balmer lines similar to the ones present in a pre-outburst spectrum. During the outburst, the $\\rm H\\alpha$ and $\\rm H\\beta$ emission lines develop a secondary peak. We also report on the discovery of two transients with similar light curve evolution and spectra: Gaia16aka and Gaia16ajq. We consider possible scenarios to explain the observed outbursts. We exclude that the transient event could be caused by a microlensing event, variable dust absorption or a tidal encounter between a neutron star and a stellar mass black hole in the accretion disk. We consider variability in the accretion flow in the inner part of the disk, or a tidal disruption event of a star $\\geq 1 M_{\\odot}$ by a rapidly spinning supermassive black hole as the most plausible scenarios. We note that the similarity between the light curves of the three Gaia transients may be a function of the Gaia alerts selection criteria.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-01-21T11:14:20.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "active galactic nucleus",
      "extreme variability",
      "spinning supermassive black hole",
      "stellar mass black hole",
      "broad balmer lines similar"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 21,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}