The Jets of TeV Blazars at Higher Resolution: 43 GHz and Polarimetric VLBA Observations from 2005-2009

TL;DR

This study uses high-resolution VLBA imaging at 43 and 22 GHz to analyze the parsec-scale structures and polarization of six TeV blazars, revealing detailed jet features and constraining jet speeds and Lorentz factors.

Contribution

It provides the highest resolution images to date of these blazars' jets, revealing new components and polarization structures, and offers improved constraints on jet speeds and Lorentz factors.

Findings

Detected new jet components within 0.2 mas of the core.

Placed upper limits on apparent speeds of less than 2c.

Revealed limb-brightening and spine-sheath polarization structures.

Abstract

We present 23 new VLBA images of the six established TeV blazars Markarian 421, Markarian 501, H 1426+428, 1ES 1959+650, PKS 2155-304, and 1ES 2344+514, obtained from 2005 to 2009. Most images were obtained at 43 GHz, and they reveal the parsec-scale structures of three of these sources (1ES 1959+650, PKS 2155-304, and 1ES 2344+514) at factors of two to three higher resolution than has previously been attained. Most of the remaining images map the linear polarization structures at a lower frequency of 22 GHz. We discuss the transverse structures of the jets as revealed by the high-frequency and polarimetric imaging. The transverse structures include significant limb-brightening in Mrk 421, and spine-sheath structures in the electric vector position angle (EVPA) and fractional polarization distributions in Mrk 421, Mrk 501, and 1ES 1959+650. We use new measured component positions to update measured apparent jet speeds, in many cases significantly reducing the statistical error over previously published results. With the increased resolution at 43 GHz, we detect new components within 0.1-0.2 mas of the core in most of these sources. No motion is apparent in these new components over the time span of our observations, and we place upper limits on the apparent speeds of the components near the core of less than 2c. From those limits, we conclude that Gamma2 < Gamma1^{1/2} at about 10^5 Schwarzschild radii, where Gamma1 and Gamma2 are the bulk Lorentz factors in the TeV-emitting and 43 GHz-emitting regions, respectively, assuming that their velocity vectors are aligned.