Optical Identifications for a Sample of Rexs: Search for BL Lac Objects

Twenty six Radio Emitting X-ray Sources (REXs) have been observed in two observing runs as part of a project aimed at selecting a new and large sample of BL Lac objects (see Wolter et al. this conference). Sources were selected by cross-correlating ROSAT-PSPC public images against VLA radio surveys. Here we present results from the first observations of 14 sources conducted in April 1995 with a B&C spectrograph in longslit mode using a CCD-Tektronix TK-1024 AB detector at the 2.1m San Pedro Martir telescope (Mexico). Table 1 shows the data derived for the 8 confirmed REXs. X-ray fluxes are in units of erg cm−2 sec−1 in the 0.1–2.4 keV band, radio fluxes are in mJy at 5 GHz, X-ray luminosities are in erg sec−1 in the energy range 0.1–2.4 keV and radio luminosities are in erg sec−1 at 5 GHz. We assumed H o = 50 km sec−1 Mpc−1 and q o = 0. A more detailed description of individual sources will be published elsewhere.