COMPARISON OF X-RAY-SELECTED AND RADIO-SELECTED BL LACERTAE OBJECTS IN HIGH-ENERGY GAMMA-RAY OBSERVATIONS

In the course of the Compton Gamma Ray Observatory mission, the EGRET telescope has detected 14 BL Lacertae objects in high-energy gamma ray s through Phase 4. According to the BL Lac sample in Ciliegi, Bassani, & Caroli, two of these 14 sources are X-ray selected (XBL) and 10 are radio-selected (RBL); two are not listed in this sample. An examinati on of the radio fluxes and the X-ray fluxes for the BL Lac objects det ected by EGRET reveals that it seems a strong radio flux must be prese nt if high-energy gamma rays are to be detected in a BL Lac object, wh ile detection is independent of the X-ray flux of the source. This res ult is in agreement with the picture of the coaligned radio jet and X- ray jet model of the broadband properties of BL Lac objects. For the B L Lac objects listed in Ciliegi et al. that are not detected by EGRET, co-adding of the EGRET data for the undetected RBLs in such a way tha t the source positions coincide with each other yields a flux excess a t a 3.5 sigma level, but similar co-adding of the EGRET data for the u ndetected XBLs yields no flux excess.