First Detection of 350 Micron Polarization From a Radio-loud AGN

TL;DR

This paper reports the first detection of linearly polarized emission at 350 microns from the radio-loud AGN 3C 279, revealing magnetic field structures and Faraday rotation effects in the jet region.

Contribution

It presents the first measurement of submillimeter polarization from a radio-loud AGN and analyzes the magnetic field and Faraday rotation properties at multiple wavelengths.

Findings

Detected 13.3% polarization at 350 μm with EVPA of 34.7°

Polarization degree increases from 10% at 13 mm to 13% at 350 μm

Faraday rotation measure scales as λ^{-2.2}

Abstract

We report the first detection of linearly polarized emission at an observing wavelength of 350 $\mu$m from the radio-loud Active Galactic Nucleus 3C 279. We conducted polarization observations for 3C 279 using the SHARP polarimeter in the Caltech Submillimeter Observatory on 2014 March 13 and 14. For the first time, we detected the linear polarization with the degree of polarization of 13.3\%$\pm$3.4\% ($3.9\sigma$) and the Electric Vector Position Angle (EVPA) of 34.7$^\circ\pm5.6^\circ$. We also observed 3C~279 simultaneously at 13, 7, and 3.5 mm in dual polarization with the Korean very long baseline interferometry (VLBI) Network on 2014 March 6 (single dish) and imaged in milliarcsecond (mas) scales at 13, 7, 3.5, and 2.3 mm on March 22 (VLBI). We found that the degree of linear polarization increases from 10\% to 13\% at 13 mm to 350 $\mu$m and the EVPAs at all observing frequencies are parallel within $<10^\circ$ to the direction of the jet at mas scale, implying that the integrated magnetic fields are perpendicular to the jet in the innermost regions. We also found that the Faraday rotation measures RM are in a range of $-6.5\times10^2 \sim -2.7\times10^3$ rad m$^{-2}$ between 13 and 3.5 mm, and are scaled as a function of wavelength: $|{\rm RM}|\propto\lambda^{-2.2}$. These results indicate that the mm and sub-mm polarization emission are generated in the compact jet within 1~mas scale and affected by a Faraday screen in or in the close proximity of the jet.