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Description
This paper presents 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, multifrequency flux values, and luminosities for each source. In addition, the different characteristics of 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 are collected through an extensive bibliographic and database search or calculated by us. The redshifts range from 0.031 to 0.702 with a maximum of the distribution at z=0.223. The 1.4GHz luminosities of XBLs log{nu}L_{nu}_~39-42erg/s while optical V and X-ray 0.1-2.4keV bands show log{nu}L_{nu}_~43-46erg/s. The XBL hosts are elliptical galaxies with effective radii r_eff_=3.26-25.40kpc and ellipticities, {epsilon}=0.04-0.52. Their R-band absolute magnitudes M_R_ range from -21.11mag to -24.86mag with a mean value of -22.83mag. The V-R indices of the hosts span from 0.61 to 1.52 and reveal a fourth-degree polynomial relationship with z that enables us 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 7.31mag for M_R_ with the highest luminosity corresponding to M_R_=-27.24mag. The masses of central BHs are found in the interval logM_BH_=7.39-9.30 solar masses (with distribution maximum at logM_BH_/M_{sun}_=8.30). The synchrotron peak frequencies are spread over the range log{nu}_peak_=14.56-19.18Hz with a peak of the distribution at log{nu}_peak_=16.60Hz. The broadband radio-to-optical ({alpha}_ro_), optical-to-X-ray ({alpha}_ox_), and radio-to-X-ray ({alpha}_rx_) 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 1.82mag through the R, V, B bands of Johnson-Cousins system, respectively. XBLs seem be optically less variable at the intranight timescales compared to the radio-selected BL Lacs (RBLs).
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