2013AJ....145...31K

This paper presents a catalog of 312 X-ray selected BL Lacerate 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 1.4 GHz luminosities of XBLs log νL_ν∼ 39-42 erg.s^–1 while optical V and X-ray 0.1-2.4 keV bands show log νL_ν∼ 43-46 erg.s^–1. The XBL hosts are elliptical galaxies with effective radii r_eff= 3.2625.40 kpc and ellipticities, ∈ = 0.040.52. Their R-band absolute magnitudes M_R range from -21.11 mag to -24.86 mag with a mean value of -22.83 mag. 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 irredshifts values are either not found or not confirmed. The XBL nuclei show a wider range of 7.31 mag for M_R with the highest luminosity corresponding to M_R= -27.24 mag. The masses of central BHs are found in the interval log M_BH= 7.39-9.30 solar masses (with distribution maximum at log M_BH/M_☉= 8.30). The synchrotron peak frequencies are spread over the range log ν_peak= 14.56-19.18 Hz with a peak of the distribution at log ν_peak= 16.60 Hz. The broadband radio-to-optical (α_ro), optical-to-X-ray (α_ox), and radio-to-X-ray (α_ 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: < Δm > = 1.22, 1.50, and 1.82 mag 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).