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We report the results of our optical (VRI) photometric observations of the TeV blazar 1ES 0806+524 on 153 nights during 2011–2019 using seven optical telescopes in Europe and Asia. We investigated the variability of the blazar on intraday as well as on long-term timescales. We examined 18 intraday light curves for flux and color variations using the most reliable power-enhanced F-test and the nested ANOVA test. Only on one night was a small, but significant, variation found, in both V-band and R-band light curves. The V−R color index was constant on every one of those nights. Flux density changes of around 80% were seen over the course of these eight years in multiple bands. We found a weighted mean optical spectral index of 0.639 ± 0.002 during our monitoring period by fitting a power law () in 23 optical (VRI) spectral energy distributions of 1ES 0806+524. We discuss different possible mechanisms responsible for blazar variability on diverse timescales. [ABSTRACT FROM AUTHOR]

Here we report on the results of the Whole Earth Blazar Telescope photo-polarimetric campaign targeting the blazar S5 0716+71, organized in 2014 March to monitor the source simultaneously in BVRI and near-IR filters. The campaign resulted in an unprecedented data set spanning ∼110 hr of nearly continuous, multiband observations, including two sets of densely sampled polarimetric data mainly in the R filter. During the campaign, the source displayed pronounced variability with peak-to-peak variations of about 30% and “bluer-when-brighter” spectral evolution, consisting of a day-timescale modulation with superimposed hour-long microflares characterized by ∼0.1 mag flux changes. We performed an in-depth search for quasi-periodicities in the source light curve; hints for the presence of oscillations on timescales of ∼3 and ∼5 hr do not represent highly significant departures from a pure red-noise power spectrum. We observed that, at a certain configuration of the optical polarization angle (PA) relative to the PA of the innermost radio jet in the source, changes in the polarization degree (PD) led the total flux variability by about 2 hr; meanwhile, when the relative configuration of the polarization and jet angles altered, no such lag could be noted. The microflaring events, when analyzed as separate pulse emission components, were found to be characterized by a very high PD (>30%) and PAs that differed substantially from the PA of the underlying background component, or from the radio jet positional angle. We discuss the results in the general context of blazar emission and energy dissipation models. [ABSTRACT FROM AUTHOR]