A Recollimation Shock in a Stationary Jet Feature with Limb-brightening in the Gamma-ray Emitting Narrow-line Seyfert 1 Galaxy 1H 0323+342

TL;DR

This paper reports the discovery of a recollimation shock in the jet of the gamma-ray-emitting NLS1 galaxy 1H 0323+342, with limb-brightening and potential gamma-ray emission linked to jet dynamics.

Contribution

It provides the first evidence of a recollimation shock in a NLS1 galaxy jet, highlighting its role in gamma-ray emission and jet structure.

Findings

Identification of a convergence site at ~100 pc from the core.

Detection of limb-brightened jet structures near the shock.

Correlation between jet features and gamma-ray activity.

Abstract

We report the discovery of a local convergence of a jet cross section in the quasi-stationary jet feature in the gamma-ray-emitting narrow-line Seyfert 1 galaxy (NLS1) 1H 0323+342. The convergence site is located at approximately 7 mas (corresponding to the order of 100 pc in deprojection) from the central engine. We also found limb-brightened jet structures at both the upstream and downstream of the convergence site. We propose that the quasi-stationary feature showing the jet convergence and limb-brightening occurs as a consequence of recollimation shock in the relativistic jets. The quasi-stationary feature is one of the possible gamma-ray-emitting sites in this NLS1, in analogy with the HST-1 complex in the M87 jet. Monitoring observations have revealed that superluminal components passed through the convergence site and the peak intensity of the quasi-stationary feature, which showed apparent coincidences with the timing of observed gamma-ray activities.