Detection of Polarimetric Variations Associated with the Shortest Time-Scale Variability in S5 0716$ + $714

TL;DR

This study reports the detection of extremely short 15-minute microvariability and associated polarimetric changes in the blazar S5 0716+714, providing insights into jet structure and magnetic fields.

Contribution

First detection of 15-minute optical/near-infrared microvariability with correlated polarization changes in S5 0716+714, revealing localized magnetic field alignment.

Findings

Detected 15-minute microvariability with 0.061 mag amplitude.

Observed polarization variation correlated with brightness change.

Microvariation linked to a small, magnetically aligned region.

Abstract

We present the result of near-infrared and optical observations of the BL Lac object S5 0716$ + $714 carried out by the KANATA telescope. S5 0716$ + $714 has both a long term high-amplitude variability and a short-term variability within a night. The shortest variability (microvariability) time-scale is important for understanding the geometry of jets and magnetic field, because it provides a possible minimum size of variation sources. Here, we report the detection of 15-min variability in S5 0716$ + $714, which is one of the shortest time-scales in optical and near-infrared variations observed in blazars. The detected microvariation had an amplitude of $0.061{\pm}0.005$ mag in $V$ band and a blue color of $\Delta(V-J)=-0.025{\pm}0.011$. Furthermore, we successfully detected an unprecedented, short time-scale polarimetric variation which correlated with the brightness change. We revealed that the microvariation had a specific polarization component. The polarization degree of the variation component was higher than that of the total flux. These results suggest that the microvariability originated from a small and local region where the magnetic field is aligned.