Optical Outburst of the Gamma-Ray Blazar S4 0954+658 in March-April 2011

TL;DR

This study reports optical photopolarimetric observations of the gamma-ray blazar S4 0954+658 during a significant outburst in 2011, highlighting rapid variability, polarization rotation, and a correlation with gamma-ray activity.

Contribution

First detailed optical polarization and brightness monitoring of S4 0954+658 during its 2011 outburst, revealing rapid variability and polarization rotation linked to flux changes.

Findings

Rapid intranight brightness increase (~0.7 mag in 7 hours)

Smooth polarization angle rotation over 200 degrees during flux rise

No significant gamma-ray activity except a coincident flux increase on March 5, 2011

Abstract

We present optical photopolarimetric observations of the BL Lac object S4 0954+658 obtained with the 70-cm telescope in Crimea, 40-cm telescope in St.Petersburg, and 1.8-m Perkins telescope at Lowell Observatory (Flagstaff, Az). After a faint state with a brightness level R ~17.6 mag registered in the first half of January 2011, the optical brightness of the source started to rise and reached ~14.8 mag during the middle of March, showing flare-like behavior. The most spectacular case of intranight variability was observed during the night of 2011 March 9, when the blazar brightened by ~0.7 mag within ~7 hours. During the rise of the flux the position angle of optical polarization rotated smoothly over more than 200 degrees. S4 0954+658 is a gamma-ray blazar with gamma-ray flux of (5{\pm}3)x10^{-10} phot/cm^2/s according to the Fermi 11-month Catalog Extragalactic Sources. Our analysis of contemporaneous Fermi LAT data does not show any sign of increased gamma-ray activity above the detection threshold except for an elevated flux on 2011 March 5, JD2455626, coincident with the local optical maximum.