Prolonged intranight optical quiescence of the classical BL Lac object PKS 0735+178

Abstract

We report our extensive intranight optical monitoring of the well known low-energy peaked (LBL) BL Lac object PKS 0735+178. This long-term follow-up consists of R-band monitoring for a minimum duration of ˜ 4 hours, on 17 nights spanning the past 11 years (1998-2008). Intra-night optical variability (INOV) amplitude of ≥ 3% on hour-like time scale was not observed in any of the nights even though the likelihood of seeing such INOV levels in a single session of ≥ 4 hours is known to be high (˜50%) for LBLs. Our observations thus establish a peculiar long-term INOV quiescence of this radio-selected BL Lac.