| Abstract: We present the results of recent quasi-simultaneous multiband optical observations (in B, V, R, and I bands) of the blazar BL Lacertae over diverse time-scales. The source was monitored from September to October 2020 using six telescopes located across the globe, yielding a total of about 5800 photometric image frames. The blazar exhibited numerous episodes of significant intraday variability, with the variability amplitude found to increase with source brightness. On short-term timescales, the flux variability amplitudes were measured to be 85.6%, 78.9%, 93.4%, and 67.6% in the B, V, R, and I bands, respectively. The colour–magnitude analysis revealed a dominant bluer-when-brighter (BWB) trend on both intraday and short-term timescales, indicative of particle acceleration processes within the relativistic jet. Strong correlations were detected among the optical bands, with no significant interband time lags. Periodicity analysis using the Lomb–Scargle and weighted wavelet Z-transform methods suggested possible indications of quasi-periodic oscillations in the light curves. Additionally, spectral energy distributions (SEDs) constructed for nights with quasi-simultaneous four-band data yielded spectral indices ranging between 2.9 and 3.2, implying a pronounced jet contribution to the optical emission. The observed variability characteristics are discussed in the context of both intrinsic mechanisms, such as shock-in-jet processes, and potential extrinsic causes. |
