Constraints on magnetic field and particle content in blazar jets through optical circular polarization

TL;DR

This study uses optical circular polarization observations of blazars 3C 279 and PKS 1510-089 to constrain their magnetic fields and particle content, ruling out models with high magnetic fields and low positron fractions.

Contribution

First optical circular polarization measurements of PKS 1510-089 provide new constraints on magnetic fields and jet composition in blazars.

Findings

Non-detection of circular polarization constrains magnetic field strength.

High-energy emission models with high magnetic fields are excluded.

Low positron fraction models are inconsistent with observations.

Abstract

Polarization offers a unique view in the physical processes of astrophysical jets. We report on optical circular polarization observations of two famous blazars, namely 3C 279 and PKS 1510-089, at high linearly polarized states. This is the first time PKS 1510-089 is observed in optical circular polarization. While only upper limits can be extracted from our observing campaign, the non-detection of optical circular polarization allows us to provide meaningful constraints on their magnetic field strength and jet composition. We find that high-energy emission models requiring high magnetic field strength and a low positron fraction can be excluded.