AAS Meeting #193 - Austin, Texas, January 1999
Session 107. (Quasars and Blazars-) High Luminosity AGN and their Environments
Display, Saturday, January 9, 1999, 9:20am-4:00pm, Exhibit Hall 1

## [107.16] New Constraints on the Spectral Energy Distribution of Blazars from the Deep X-ray Radio Blazar Survey (DXRBS)

P. Padovani (ESA, STScI), E. S. Perlman (STScI), P. Giommi (BeppoSAX SDC), R. M. Sambruna (Penn. State University)

The Deep X-ray Radio Blazar Survey (DXRBS) will provide, when complete, a sample of about 300 blazars. The candidate list is obtained by correlating the ROSAT WGACAT database with several radio catalogs and restricting the selection to flat spectrum radio sources (\alphar \le 0.70). The selection criteria result in a very high efficiency (~ 95%) at finding flat-spectrum radio quasars and BL Lacertae objects. Identification of the sources is ~ 80% complete. One of the most interesting discoveries so far is the identification of a large population of flat-spectrum radio quasars (~25% of all DXRBS quasars) with ratios of X-ray to radio luminosity \ga 10-6 (\alpha\rm rx \la 0.78; Perlman et al. 1998). These X-ray strong'' quasars, which previous surveys could not have detected, might be the high-luminosity version of the high-energy peaked BL Lacs, which have synchrotron peak emission in the UV/X-ray band. Here we present a detailed investigation of the spectral energy distribution of this newly discovered class of blazars. We also compare our results with the predictions of recent models aimed at unifying blazars in terms of the position of the synchrotron peak and of power.