Radio Detection of 18 RASS BL Lac Objects

Abstract

We present the radio detection of 18 BL Lac objects from oursurvey of over 575 deg$^2$ of sky. These 18 objects are located within$20arcsec$ of the X-ray position, of which 11 have a measuredred-shift. All candidates are radio emitters above $sim$1 mJy and fall within the range of existing samples on the two colour, $alpha _mathrm{RO}$ vs $alpha _mathrm{OX}$, 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 $log( u _mathrm{peak})approx 19.2$. The BL Lac $log(N)-log(S)$ relation is consistent with other samples and indicates the ROSAT All Sky Survey (RASS) could contain ($2000{pm}400$) BL Lac objects.

Keywords

• Galaxies: active
• BL Lacertae objects: general
• quasars: general