Intra-night optical flux and polarization variability of BL~Lacertae during its 2020 $-$ 2021 high state

Abstract

In this work, we report the presence of rapid intra-night optical variations in both -- flux and polarization of the blazar BL Lacertae during its unprecedented 2020--2021 high state of brightness. The object showed significant flux variability and some color changes, but no firmly detectable time delays between the optical bands. The linear polarization was also highly variable in both -- polarization degree and angle (EVPA). The object was observed from several observatories throughout the world, covering in a total of almost 300 hours during 66 nights. Based on our results, we suggest, that the changing Doppler factor of an ensemble of independent emitting regions, travelling along a curved jet that at some point happens to be closely aligned with the line of sight can successfully reproduce our observations during this outburst. This is one of the most extensive variability studies of the optical polarization of a blazar on intra-night timescales.

23 pages,7 figures, 5 Tables (2 as appendix). Accepted for publication in MNRAS

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Cited by in corpus (9)

• IXPE observation of PKS 2155-304 reveals the most highly polarized blazar
• Quasi-simultaneous Optical Flux and Polarization Variability of the Binary Super Massive Black Hole Blazar OJ 287 from 2015 to 2023: Detection of an Anticorrelation in Flux and Polarization Variability
• High optical to X-ray polarization ratio reveals Compton scattering in BL Lacertae's jet
• Determining the origin of the X-ray emission in blazars through multiwavelength polarization
• Spectral Energy Distribution Modeling of BL Lacertae During a Large Submillimeter Outburst and Low X-Ray Polarization State
• Investigating the origin of optical flares from the TeV blazar S4 0954+65
• Polarization Studies in Different Blazar Types. Part I: Correlation between Optical Brightness and Polarization Degree
• Multi-band optical variability of the blazar OP 313 in the outburst state during 2024-2025
• Detection of Compton scattering in the jet of 3C 84