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 time-scale of a few days. The object favors a polarization angle (PA) of $40^{\circ }$--$50^{\circ }$ at the flare maxima, which is close to the position angle of the jet ($20^{\circ }$--$40^{\circ }$). 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 $-50^{\circ }$ to $-20^{\circ }$ 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, $\delta$. Based on this scenario, the minimum viewing angle of the source, ${\theta }_{\min }=4.8^{\circ }$--$6.6^{\circ }$, and the location of the source, $\Delta r\gtrsim 0.1$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 $\delta$. The combined effect of the variation in $\delta$ and acceleration/cooling of electrons is probably responsible for the observed diversity of the polarization variations in the flares.

12 pages, 9 figures, accepted for publication in PASJ

References in corpus (10)

• Probing the Inner Jet of the Quasar PKS 1510-089 with Multi-waveband Monitoring during Strong Gamma-ray Activity
• Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies
• A change in the optical polarization associated with a gamma-ray flare in the blazar 3C 279
• The Outburst of the Blazar AO 0235+164 in 2006 December: Shock-in-Jet Interpretation
• F-GAMMA: Variability Doppler factors of blazars from multiwavelength monitoring
• Radio Circular Polarization Produced in Helical Magnetic Fields in Eight Active Galactic Nuclei
• Systematic Study of Gamma-ray bright Blazars with Optical Polarization and Gamma-ray Variability
• RoboPol: Do optical polarization rotations occur in all blazars?
• Polarization swings in blazars
• Polarization swings from curved trajectories of the emitting regions

Cited by in corpus (10)

• RoboPol: A four-channel optical imaging polarimeter
• A comprehensive study on the variation phenomena of AO 0235+164
• Repeated pattern of gamma-ray flares in the lightcurve of the blazar 3C 279
• The RoboPol Program: Optical Polarimetric Monitoring of Blazars
• Testing particle acceleration in blazar jets with continuous high-cadence optical polarization observations
• Spectral Energy Distribution Modeling of BL Lacertae During a Large Submillimeter Outburst and Low X-Ray Polarization State
• Follow-up Observations for IceCube-170922A: Detection of Rapid Near-Infrared Variability and Intensive Monitoring of TXS 0506+056
• Distinguishing radiation mechanisms and particle populations in blazar jets through long-term multi-band monitoring with RINGO3 and Fermi
• Identifying changing jets through their radio variability
• Constraints on magnetic field and particle content in blazar jets through optical circular polarization