UBVRI photometry of Southern Sky BL Lacs

Seventeen southern sky BL Lacs were observed in UBVRI using the CCD Camera on the 1.0 m telescope at the South African Astronomical Observatory (SAAO) in Aug and Nov 1999. The analyses of all the seventeen sources are now complete, and are available via anonymous ftp (ftp.pukrs1.puk.ac.za/Blazars). A few examples of our results are however given in this paper. Whereas PKS 2005−489 and 2155−304 appear to have been in a high state, PKS 0048−097 and PKS 0521−365 showed evidence of variability on a time-scale of a few days, with the amplitude of variability increasing towards short wavelengths. This is consistent with observations of gamma-ray BL Lacs, which show similar behavior in optical and X-rays.