We report the discovery of extreme X-ray variability in a type 1 quasar : SDSS J075101.42+291419.1 .
It has a black hole mass of 1.6 \times 10 ^ { 7 } ~ { } M _ { \odot } measured from reverberation mapping ( RM ) , and the black hole is accreting with a super-Eddington accretion rate .
Its XMM-Newton observation in 2015 May reveals a flux drop by a factor of \sim 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 ( \alpha _ { 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 well the 0.3–10 keV spectra of the X-ray observations in general .
The spectral fitting reveals steep spectral shapes with \Gamma \approx 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 \approx 15 \textrm { - - } 24 \% .
We discuss two possible scenarios , disk reflection and partial covering absorption , to explain the extreme X-ray variability of SDSS J 075101.42 + 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 .