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Session 119 - QSOs and BL Lacs.
Oral session, Thursday, January 18
1st Floor, La Villita Assembly Building

[119.06] A New Sample of X-ray--Selected BL Lacertae Objects and Implications for Unified Schemes

S. A. Laurent-Muehleisen (PSU)

We present a well-defined sample of \sim30 new BL Lacertae Objects discovered in the Rosat All-Sky Survey (RASS). This sample is the largest sample of X-ray--selected BL Lacertae Objects (XBLs) yet created from the RASS and increases the number of XBLs that were known prior to the Rosat mission by nearly 50%. The objects were discovered among the >2,000 sources with entries in both the RASS and GreenBank 5 GHz radio catalogs (Gregory amp; Condon 1991). Our followup high resolution VLA observations of these Rosat-GreenBank sources produced a database of subarcsecond positions and core radio fluxes which were correlated with POSS I plates, giving broadband radio, optical and X-ray colors. Following the method of Schachter et al.\, (1993), we concentrated our followup spectroscopic observations on objects with flat radio--optical and optical--X-ray spectral indices, although other objects were observed to assess biases in this selection criterion. All together 177 objects brighter than B \approx 18.5 were observed at low spectroscopic resolution. Approximately 60% of these sources are quasars, 15% are radio galaxies and 25% are BL Lacertae objects. We combine our newly discovered objects with previously known objects which match our selection criteria and present a well-defined sample of \sim60 BL Lacertae objects. These BL Lacertae objects are presented on a LogN-LogS diagram and compared to previous results from other surveys and the implications for beaming models and cosmic evolution are discussed.

\beginsmall Gregory amp; Condon, 1991, ApJS, 75, 1011 \hspace*0.15inSchachter, et al.\, ApJ, 412, 541 \endsmall

Program listing for Thursday