Abstract:
In this paper we present the results of a short-term optical monitoring program of 13 blazars.
The objects were monitored mostly in the R band for a total of ∼160 h between 2006 and
2011. We study the nature of the short-term variations and show that most of them could be
described as slow, smooth and (almost) linear changes of up to ∼0.1 mag h⁻¹, but that many
objects show no short-term variations at all. In fact, we found only a ∼2 per cent chance of
observing variability of more than 0.1 mag h⁻¹ for the sample we observed. Hints of quasiperiodic
oscillations at very low-amplitude levels are also found for some objects. We briefly
discuss some of the possible mechanisms for generating the intra-night variability and the
quasi-periodic oscillations.
