Multi-band optical variability studies of BL Lacertae

TL;DR

This study presents multi-band optical monitoring of BL Lacertae, revealing significant intraday variability, spectral flattening during brightness increases, and strong correlation between V and R band light curves, enhancing understanding of blazar variability.

Contribution

It provides detailed multi-band optical variability analysis of BL Lacertae, including spectral energy distribution and correlation studies, offering new insights into blazar spectral and flux variations.

Findings

Detected significant intraday variability on multiple nights.

Observed spectral flattening as the source brightens.

V and R band light curves are highly correlated.

Abstract

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.