Radio VLBA polarization and multi-band monitoring of the high-redshift quasar S5 0836+710 during a high activity period

TL;DR

This paper presents multi-band radio to gamma-ray observations of the high-redshift quasar S5 0836+710 during a period of intense activity, revealing gamma-ray flares, jet dynamics, and polarization structures that inform jet physics.

Contribution

It provides the first detailed polarization and multi-band monitoring of S5 0836+710 during a high activity period, linking gamma-ray flares to jet features and magnetic field configurations.

Findings

Detected two major gamma-ray flares with luminosities over 10^50 erg/s.

Identified a superluminal knot emerging during radio activity peak.

Observed a transverse rotation measure gradient indicating a toroidal magnetic field.

Abstract

We report on results of a multi-band monitoring campaign from radio to gamma rays of the high-redshift flat spectrum radio quasar S5 0836+710 during a high activity period detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Two major flares were detected, in 2015 August and November. In both episodes, the apparent isotropic gamma-ray luminosity exceeds 10^50 erg/s, with a doubling time scale of about 3 hours. The high gamma-ray activity may be related to a superluminal knot that emerged from the core in 2015 April at the peak of the radio activity and is moving downstream along the jet. The low variability observed in X-rays may indicate that X-ray emission is produced by the low-energy tail of the same electron population that produces the gamma-ray emission. The analysis of full-polarization pc-scale radio observations suggests the presence of a limb-brightened polarization structure at about 1 mas from the core in which a rotation measure gradient with a sign change is observed transverse to the jet direction. These characteristics are consistent with a scenario in which Faraday rotation is produced by a sheath of thermal electrons with a toroidal magnetic field surrounding the emitting jet.