SDSS J075101.42+291419.1: A Super-Eddington Accreting Quasar with Extreme X-Ray Variability

Hezhen Liu, B. Luo, W. N. Brandt, Michael S. Brotherton, Pu Du, S. C. Gallagher, Chen Hu, Ohad Shemmer, Jian Min Wang

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6 Scopus citations

Abstract

We report the discovery of extreme X-ray variability in a type 1 quasar: SDSS J075101.42+291419.1. It has a black hole (BH) mass of 1.6 × 107 M o measured from reverberation mapping, and the BH is accreting with a super-Eddington accretion rate. Its XMM-Newton observation in 2015 May reveals a flux drop by a factor of ∼22 with respect to the Swift observation in 2013 May when it showed a typical level of X-ray emission relative to its UV/optical emission. The lack of correlated UV variability results in a steep X-ray-to-optical power-law slope (α OX) of-1.97 in the low X-ray flux state, corresponding to an X-ray weakness factor of 36.2 at rest-frame 2 keV relative to its UV/optical luminosity. The mild UV/optical continuum and emission-line variability also suggest that the accretion rate did not change significantly. A single power-law model modified by Galactic absorption describes the 0.3-10 keV spectra of the X-ray observations well in general. The spectral fitting reveals steep spectral shapes with Γ ≈ 3. We search for active galactic nuclei (AGNs) with such extreme X-ray variability in the literature and find that most of them are narrow-line Seyfert 1 galaxies and quasars with high accretion rates. The fraction of extremely X-ray variable objects among super-Eddington accreting AGNs is estimated to be ≈15%-24%. We discuss two possible scenarios, disk reflection and partial covering absorption, to explain the extreme X-ray variability of SDSS J075101.42+291419.1. We propose a possible origin for the partial covering absorber, which is the thick inner accretion disk and its associated outflow in AGNs with high accretion rates.

Original languageEnglish (US)
Article number79
JournalAstrophysical Journal
Volume878
Issue number2
DOIs
StatePublished - Jun 20 2019

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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