VLBI Imagings of Kilo-parsec Knot in 3C 380

TL;DR

This study uses high-resolution VLBI imaging to analyze a kilo-parsec scale knot in quasar 3C 380, revealing detailed morphology and constraining its apparent velocity, which is slightly below superluminal speeds.

Contribution

It provides the highest resolution VLBI images of the knot K1 in 3C 380 and offers new insights into its structure and kinematics, including an upper limit on its apparent velocity.

Findings

Revealed an inverted bow-shock structure in K1.

Achieved three times better resolution than previous images.

Estimated an upper limit of 9.8c for K1's apparent velocity.

Abstract

We investigate observational properties of a kilo-parsec scale knot in radio-loud quasar 3C 380 by using two epoch archival data obtained by Very Long Baseline Interferometry (VLBI) at 5 GHz on 1998 July and 2001 April. We succeed in obtaining the highest spatial resolution image of the bright knot K1 located at 732 milliarcseconds, or more than 20 kpc de-projected, downstream from the nucleus three times better than previously obtained highest resolution image by Papageorgiou et al. (2006). Our images reveal, with new clarity, "inverted bow-shock" structure in K1 facing the nucleus and its morphology resembles a conical shock wave. By comparing the two epoch images directly, we explore the kinematics of K1 and obtain the upper limit of apparent velocity, 0.25 mas/yr or 9.8 c of K1 for the first time. The upper limit of apparent velocity is marginally smaller than superluminal motions seen in the core region. Further new epoch VLBI observations are necessary to measure the proper motion at K1.