Analysis of the Intranight Variability of BL Lacertae during Its 2020 August Flare

Abstract We present an analysis of the BVRI photometry blazar BL Lacertae on diverse timescales from 2020 mid-July to mid-September. have used 11 different optical telescopes around world and collected data over 84 observational nights. The observations cover onset a new activity phase that started in August (termed as flare by us), is focused intranight variability. On short-term timescales, (i) flux varied with ∼2.2 mag R band, (ii) spectral index was found be weakly dependent (i.e., variations could considered mildly chromatic), (iii) no periodicity detected. predominantly show bluer-when-brighter chromatism. also two cases significant interband time lags order few minutes. duty cycle during estimated quite high (∼90% or higher). decomposed light curves into individual flares determined their characteristics. basis our assuming turbulent jet model, we some characteristics emitting regions: Doppler factor, magnetic field strength, electron Lorentz radius. radii were discussed framework Kolmogorov theory turbulence. weighted mean structure function slope related it power density, regard origin