Short Term Flux and Colour Variations in Low-Energy Peaked Blazars
  We have measured multi-band optical flux and colour variations for a sample
of 12 low energy peaked blazars on short, day-to-month, timescales. Our sample
contains six BL Lacertae objects and six flat spectrum radio quasars. These
photometric observations, made during September 2008 to June 2009, used five
optical telescopes, one in India and four in Bulgaria. We detected short term
flux variations in eleven of these blazars and colour variability in eight of
them. Our data indicate that six blazars (3C 66A, AO 0235+164, S5 0716+714, PKS
0735+178, OJ 287 and 3C 454.3) were observed in pre- or post-outburst states,
that five (PKS 0420-014, 4C 29.45, 3C 279, PKS 1510-089 and BL Lac) were in a
low state, while one (3C 273) was in an essentially steady state. The duty
cycles for flux and colour variations on short timescales in these low energy
peaked blazars are ~ 92 percent and ~ 33 percent, respectively. The colour vs
magnitude correlations seen here support the hypothesis that BL Lac objects
tend to become bluer with increase in brightness; however, flat spectrum radio
quasars may show the opposite trend, and there are exceptions to these trends
in both categories of blazar. We briefly discuss emission models for active
galactic nuclei that might explain our results.
