Abstract:
We present the results of extensive multiband intranight optical monitoring of BL Lacertae
during 2010–2012. BL Lacertae was very active in this period and showed intense variability
in almost all wavelengths. We extensively observed it for a total for 38 nights; on 26 of them,
observations were done quasi-simultaneously in B, V, R and I bands (totalling 113 light curves),
with an average sampling interval of around 8 min. BL Lacertae showed significant variations
on hour-like time-scales in a total of 19 nights in different optical bands. We did not find
any evidence for periodicities or characteristic variability time-scales in the light curves. The
intranight variability amplitude is generally greater at higher frequencies and decreases as the
source flux increases.We found spectral variations in BL Lacertae in the sense that the optical
spectrum becomes flatter as the flux increases but in several flaring states, deviates from the
linear trend suggesting different jet components contributing to the emission at different times.
