Multi-band optical variability studies of BL Lacertae
  We monitored BL Lacertae for 13 nights in optical B, V, R, and I bands during
October and November 2014 including quasi-simultaneous observations in V and R
bands using two optical telescopes in India. We have studied multi-band optical
flux variations, colour variation and spectral changes in this blazar. Source
was found to be active during the whole monitoring period and showed
significant intraday variability on 3 nights in V and R filters while displayed
hints of variability on 6 other dates in R passband and on 2 nights in V
filter. From the colour-magnitude analysis of the source we found that the
spectra of the target gets flatter as it becomes brighter on intra-night
timescale. Using discrete correlation technique, we found that intraday light
curves in both V and R filters are almost consistent and well correlated with
each other. We also generated spectral energy distribution (SED) of the target
using the B, V, R, and I data sets for all 13 nights which could help us
investigate the physical process responsible for the observed variations in BL
Lacertae objects. We also discuss possible physical causes of the observed
spectral variability.
