Multi-Band Intra-Night Optical Variability of BL Lacertae

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.

15 pages, 5 Figures, 3 Tables; Accepted for publication in Galaxies; a special issue on Microvariability of Blazars

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• Fast TeV variability in blazars: jets in a jet
• Multi-colour optical monitoring of eight red blazars
• Multi-band optical variability studies of BL Lacertae
• Longterm Optical Monitoring of Bright BL Lacertae Objects with ATOM: Spectral Variability and Multiwavelength Correlations
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• X-ray Flux and Spectral Variability of Blazar H 2356-309