  Precise measurements of black hole (BHs) masses are necessary to understand
the coevolution of these sources and their host galaxies. Sometimes in the
center of a galaxy there is not one, but two BHs. The BH duality of the quasar
nucleus SDSS~J075217.84+193542.2 (herein SDSS~J0752) was recently proposed
based on the observed strict periodicity of optical emission from the source.
We tested this assumption using X-ray observations with Swift/XRT (2008--2010).
We fitted the SDSS~J075217 spectrum using a Comptonization model and discovered
soft X-ray variability in the 0.3--10~keV energy range. We pursued a scenario
in which two supermassive BHs at the center of SDSS~J0752 form a pair; and the
less massive (secondary) BH periodically crosses/punctures the disk around the
more massive (primary) BH. We associate these periodic crossings with tidal
disruptions of the disk and, as a consequence, with an increase in X-rays seen
as a flare in SDSS~J0752. During such an X-ray flare event (2008--2010), we
discovered a change in the source spectral states and the photon index
saturation at the $\Gamma\sim3$ level with mass accretion rate $\dot M$. For BH
mass scaling we used sources: OJ~287, M101 ULX--1 and HLX--1 ESO~243--49, as a
reference ones, and found that M$_{SDSS}=9\times 10^7$ solar masses, assuming
$d_{SDSS}= 500$ Mpc. Thus, we obtained a lower limit to a BH mass due the
unknown inclination. In addition, we used the virial mass of the secondary BH
based on $H_\alpha$-line measurements and we estimated the binary's inclination
at SDSS~J0752, $i=80^{\circ}$, using a scaling technique.
