Multifrequency Photo-polarimetric WEBT Observation Campaign on the Blazar S5 0716+714: Source Microvariability and Search for Characteristic Timescales

TL;DR

This paper presents a comprehensive multi-band and polarimetric observational campaign of blazar S5 0716+714, revealing rapid microvariability, spectral evolution, and polarization behavior, while searching for characteristic timescales and polarization-flux correlations.

Contribution

It provides the first extensive multi-band, nearly continuous dataset with polarimetric data for this blazar, analyzing microflares, spectral changes, and polarization-flux relationships in detail.

Findings

Detected microflares with ~0.1 mag flux changes and high polarization (>30%).

Found potential ~3h and ~5h quasi-periodic oscillation hints, not statistically significant.

Observed polarization degree changes leading flux variability by about 2 hours under certain conditions.

Abstract

Here we report on the results of the WEBT photo-polarimetric campaign targeting the blazar S5~0716+71, organized in March 2014 to monitor the source simultaneously in BVRI and near IR filters. The campaign resulted in an unprecedented dataset spanning $\sim 110$\,h of nearly continuous, multi-band observations, including two sets of densely sampled polarimetric data mainly in 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 hourlong microflares characterized by $\sim 0.1$\,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 $\sim 3$\,h and $\sim 5$\,h 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 relative to the positional angle of the innermost radio jet in the source, changes in the polarization degree led the total flux variability by about 2\,h; 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 polarization degree ($> 30\%$) and polarization angles which differed substantially from the polarization angle 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.