Systematic Study of Gamma-ray bright Blazars with Optical Polarization and Gamma-ray Variability

TL;DR

This study investigates the relationship between optical polarization and gamma-ray variability in blazars, revealing differences in magnetic field alignment across blazar subclasses through simultaneous multi-wavelength observations.

Contribution

It provides the first systematic analysis linking optical polarization degrees with gamma-ray luminosity and flux ratios in a large sample of blazars.

Findings

Correlation between maximum optical polarization and gamma-ray luminosity.

Differences in magnetic field alignment between blazar subclasses.

Implications for jet composition and magnetic field structure.

Abstract

Blazars are highly variable active galactic nuclei which emit radiation at all wavelengths from radio to gamma-rays. Polarized radiation from blazars is one key piece of evidence for synchrotron radiation at low energies and it also varies dramatically. The polarization of blazars is of interest for understanding the origin, confinement, and propagation of jets. However, even though numerous measurements have been performed, the mechanisms behind jet creation, composition and variability are still debated. We performed simultaneous gamma-ray and optical photopolarimetry observations of 45 blazars between Jul. 2008 and Dec. 2014 to investigate the mechanisms of variability and search for a basic relation between the several subclasses of blazars. We identify a correlation between the maximum degree of optical linear polarization and the gamma-ray luminosity or the ratio of gamma-ray to optical fluxes. Since the maximum polarization degree depends on the condition of the magnetic field (chaotic or ordered), this result implies a systematic difference in the intrinsic alignment of magnetic fields in pc-scale relativistic jets between different types blazars (FSRQs vs. BL Lacs), and consequently between different types of radio galaxies (FR Is vs. FR IIs).