This table contains a catalog of 312 X-ray selected BL Lacertae objects (XBLs), optically identified through the end of 2011. It contains the names from different surveys, equatorial coordinates, redshifts, multi-frequency flux values, and luminosities for each source. In the reference, the different characteristics of these XBLs are statistically investigated (redshift, radio/optical/X-ray luminosities, central black hole (BH) mass, synchrotron peak frequency, broadband spectral indices, optical flux variability). Their values were collected through an extensive bibliographic and database search or calculated by the author. The redshifts range from 0.031 to 0.702 with a maximum of the distribution at z = 0.223. The 1.4-GHz luminosities of XBLs log (nu * L<sub>nu</sub>) ~ 39 - 42 (in units of erg s<sup>-1</sup>), while the optical V and X-ray (0.1-2.4 keV) bands show log (nu * L<sub>nu</sub>) ~ 43 - 46 (same units). The XBL hosts are elliptical galaxies with effective radii r<sub>eff</sub> = 3.26 - 25.40 kpc and ellipticities e = 0.04 - 0.52. Their R-band absolute magnitudes M<sub>R</sub> range from -21.11 mag to -24.86 mag with a mean value of -22.83 mag. The V - R indices of the hosts range from 0.61 to 1.52 and reveal a fourth-degree polynomial relationship with z that enabled the author to evaluate the redshifts of five sources whose V - R indices were determined from the observations, but whose redshifts values are either not found or not confirmed. The XBL nuclei show a wider range of 7.31 mag for M<sub>R</sub>, with the highest luminosity corresponding to M<sub>R</sub> = -27.24 mag. The masses of the central BHs are found in the interval log M<sub>BH</sub> = 7.39 - 9.30 (in units of solar masses), with the maximum of the distribution at log M<sub>BH</sub>/M<sub>sun</sub> = 8.30. The synchrotron peak frequencies are spread over the range log nu<sub>peak</sub> = 14.56 - 19.18 Hz, with a peak of the distribution at log nu<sub>peak</sub> = 16.60 Hz. The broad-band radio-to-optical (alpha<sub>ro</sub>), optical-to-X-ray (alpha<sub>ox</sub>), and radio-to-X-ray (alpha<sub>rx</sub>) spectral indices are distributed in the intervals (0.17, 0.59), (0.56, 1.48), and (0.41, 0.75), respectively. In the optical energy range, the overall flux variability increases, on average, towards shorter wavelengths: Delta(m) = 1.22, 1.50, and 1.82 through the R, V, B bands of the Johnson-Cousins system, respectively. XBLs seem be optically less variable at intranight timescales compared to radio-selected BL Lacs (RBLs). This table was created by the HEASARC in June 2013 based on an electronic version of Table 2 from the reference paper which was obtained form the AJ web site. This is a service provided by NASA HEASARC .
