Abstract:
We monitored BL Lacertae for 13 nights in optical B, V, R, and I bands during 2014 October
and November including quasi-simultaneous observations in V and R bands using two optical
telescopes in India. We have studied multiband 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 three nights in V and R filters while
displayed hints of variability on six other dates in R passband and on two nights in V filter.
From the colour–magnitude analysis of the source, we found that the spectra of the target get
flatter as it becomes brighter on intranight time-scale. 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 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.
