Optical and X-ray cutouts, as in Fig. 2, for three of the four newly-discovered X-ray counterparts of MBH candidates, complemented by the fourth new X-ray detection shown as example in Fig. 2. The left panels show SDSS J031302.15-004110.9 at RA, Dec = (48.25895, −0.686379) and z = 0.131, the middle panels SDSS J121709.27+122714.4 (Ra, Dec: 184.28861, 12.45432) at z = 0.007 and the right panels SDSS J130717.44+133847.8 (Ra, Dec: 196.822679, 13.646658) at z = 0.027, respectively. We note that the positional accuracy of the X-ray centroid is 1.5″, 3.5″ and 2.4″ from left to right, respectively. More details on their association are presented in Sect. 5.3.