Optical polarization variations in the blazar PKS 1749+096

Abstract

We report on the variation in the optical polarization of the blazar PKS 1749+096 observed in 2008-2015. The degree of polarization (PD) tends to increase in short flares having a timescale of a few days. The object favors a polarization angle (PA) of 40 • -50 • at the flare maxima, which is close to the position angle of the jet (20 • -40 • ). Three clear polarization rotations were detected in the negative PA direction associated with flares. In addition, a rapid and large decrease in the PA was observed in the other two flares, while another two flares showed no large PA variation. The light curve maxima of the flares possibly tend to lag behind the PD maxima and color-index minima. The PA became −50 • to −20 • in the decay phase of active states, which is almost perpendicular to the jet position angle. We propose a scenario to explain these observational features, where transverse shocks propagate along curved trajectories. The favored PA at the flare maxima suggests that the observed variations were governed by the variations in the Doppler factor, δ. Based on this scenario, the minimum viewing angle of the source, θ min = 4.8 • -6.6 • , and the location of the source, ∆r > ∼ 0.1 pc, from the central black hole were estimated. In addition, the acceleration of electrons by the shock and synchrotron cooling would have a time-scale similar to that of the change in δ. The combined effect of the variation in δ and acceleration/cooling of electrons is probably responsible for the observed diversity of the polarization variations in the flares.

Follow-up Observations for IceCube-170922A: Detection of Rapid Near-Infrared Variability and Intensive Monitoring of TXS 0506+056

“…The lack of strong correlations between optical brightness and polarization degree in our data for TXS 0506+056 is similarly observed in previous literature for other blazars (Ikejiri et al 2011;Jermak et al 2016), although a significant positive correlation between "amplitudes" of flux and polarization degree is detected for two blazars (AO 0235+164 and PKS 1510-089) in 10-day time scale (Sasada et al 2011). These observed weak correlations could be partly due to ignorance of a possible time lag be-tween temporal changes of fluxes and polarization degrees (Uemura et al 2017). Figure 11 is a magnified view of Figure 4 around the second epoch.…”

Identifying changing jets through their radio variability

“…Individual flares, can nevertheless yield both higher and lower δ var . Changes in the viewing angle by factors of two to three during individual events have been noted in previous studies (e.g., Larionov et al 2010;Raiteri et al 2017;Uemura et al 2017;.…”

Identifying changing jets through their radio variability

“…Individual flares, can nevertheless yield both higher and lower δ var . Changes in the viewing angle by factors of 2-3 during individual events have been noted in previous studies (e.g., Larionov et al 2010;Raiteri et al 2017;Uemura et al 2017;. Variations in other geometric and physical parameters of the emission region (e.g., Lorentz factor, magnetic field strength etc.)…”