Optical flux and spectral variability of BL Lacertae during its historical high outburst in 2020

Nibedita Kalita, Yuhai Yuan, Minfeng Gu +9

BL Lacertae had undergone a series of historical high flux activity over a year, from August 2020 in the optical to VHE $\gamma$-rays. In this paper, we report on optical flux and spect…