Parsec-scale Structure and Kinematics of Faint TeV HBLs

TL;DR

This study uses VLBA observations to analyze the parsec-scale structure and motion of faint TeV HBLs, revealing for the first time a superluminal component in their jet speeds.

Contribution

It provides new multi-epoch VLBA measurements of TeV HBLs, uncovering superluminal jet speeds previously unobserved in these faint sources.

Findings

Detection of superluminal jet speeds in TeV HBLs

Most sources show subluminal or barely superluminal speeds

Enhanced understanding of jet velocity structures in faint blazars

Abstract

We present new multi-epoch Very Long Baseline Array (VLBA) observations of a set of TeV blazars drawn from our VLBA program to monitor all TeV-detected high-frequency peaked BL Lac objects (HBLs) at parsec scales. Most of these sources are faint in the radio, so they have not been well observed with VLBI by other surveys. Our previous measurements of apparent jet speeds in TeV HBLs showed apparent jet speeds that were subluminal or barely superluminal, suggesting jets with velocity structures at the parsec-scale. Here we present apparent jet speed measurements for eight new TeV HBLs, which for the first time show a superluminal tail to the apparent speed distribution for the TeV HBLs.