2011MNRAS.413.2157R

We have carried out optical (R band) intraday variability (IDV) monitoring of a sample of 10 bright low energy peaked blazars (LBLs). 40 photometric observations, of an average of ∼4 h each, were made between 2008 September and 2009 June using two telescopes in India. Measurements with good signal-to-noise ratios were typically obtained within 1–3 min, allowing the detection of weak, fast variations using N-star differential photometry. We employed both structure function and discrete correlation function analysis methods to estimate any dominant time-scales of variability and found that in most of the cases any such time-scales were longer than the duration of the observation. The calculated duty cycle of IDV in LBLs during our observing run is ∼52 per cent, which is low compared to many earlier studies; however, the relatively short periods for which each source was observed can probably explain this difference. We briefly discuss possible emission mechanisms for the observed variability.