Аннотация:We presented a study of outburst activity in the BL Lacertae source OJ 287, observed extensively with the X-ray telescope (XRT) onboard Neil Gehrels Swift Observatory.We demonstrated that the results of our analysis of X-ray flaring activity using the Swift/XRT data allow to refine the key characteristics of the OJ 287 secondary (its nature and mass). We discovered that the energy spectra in all spectral states can be fitted using the XSPEC Bulk Motion Comptonization (BMC) model. As a result we found that the X-ray photon index of the BMC model, Г correlates with the mass accretion rate, ˙M. We established that Г increases monotonically with ˙M from the low-hard state, Г~1.5 to the high-soft state, Г~2.8 and finally saturates. The index behavior was similar to that in a number of black hole (BH) candidates in which we showed that its saturation was an observational evidence of the presence of a BH. Based on this correlation, we applied a scaling method and determined that a secondary BH mass in OJ 287 is about 1.25*10^8 solar masses, using the well-studied X-ray BH binaries XTE 1550–564, H 1743–322, 4U 1630–47, GRS 1915+105 as well as extragalactic BHs ESO 243–49 and M101 ULX–1, as reference sources. Also using the power spectrum analysis we inferred the size of the Compton cloud L_CC~10^13 cm where X-ray spectra were formed. Using this value of L_CC we confirmed that a BH mass of the secondary in OJ 287 was of order of 108 solar masses as we derived using the index, Г-correlation (the scaling method) with respect of the mass accretion rate.