Multi-Band Intra-Night Optical Variability of BL Lacertae

TL;DR

This study monitored BL Lacertae over multiple nights, revealing significant intra-day optical variability, spectral changes correlated with brightness, and insights into the source's variability behavior without identifying periodic patterns.

Contribution

It provides detailed multi-band intra-night variability analysis of BL Lacertae, highlighting spectral changes and variability characteristics during high states.

Findings

Significant intra-day variability observed on 13 nights.

Optical spectrum becomes bluer when brighter.

No periodicities or characteristic time-scales detected.

Abstract

We monitored BL Lacertae frequently during 2014 - 2016 when it was generally in a high state. We searched for intra-day variability for 43 nights using quasi-simultaneous measurements in the B, V, R, and I bands (totaling 143 light curves); the typical sampling interval was about eight minutes. On hour-like timescales, BL Lac exhibited significant variations during 13 nights in various optical bands. Significant spectral variations are seen during most of these nights such that the optical spectrum becomes bluer when brighter. The amplitude of variability is usually greater for longer observations but is lower when BL Lac is brighter. No evidence for periodicities or characteristic variability time-scales in the light curves was found. The color variations are mildly chromatic on long timescales.