Radio detection of 18 RASS BL Lac objects

We present the radio detection of 18 BL Lac objects from our survey of over 575 deg2 of sky. These 18 objects are located within 20'' of the X-ray position, of which 11 have a measured red-shift. All candidates are radio emitters above ~1 mJy and fall within the range of existing samples on the two colour, αRO vs αOX, diagram with a transitional population of three evident. Two unusual sources have been identified, a candidate radio quiet BL Lac, RX J0140.9-4130, and an extreme HBL, RX J0109.9-4020, with log (νpeak) ≈19:2. The BL Lac log(N)-log(S) relation is consistent with other samples and indicates the ROSAT All Sky Survey (RASS) could contain (2000±400) BL Lac objects