TXS 0128+554: A Young Gamma-Ray Emitting AGN With Episodic Jet Activity

TL;DR

This study reveals that TXS 0128+554 is a very young, episodic jet AGN with gamma-ray emission likely originating from its inner jet, supported by multi-frequency X-ray and radio observations.

Contribution

It provides the first detailed multi-frequency analysis of TXS 0128+554, demonstrating its episodic jet activity and young age, and discusses the origin of its gamma-ray emission.

Findings

TXS 0128+554 is among the youngest CSOs with an age of about 82 years.

The AGN shows episodic jet activity with re-launches within a decade.

Gamma-ray emission likely originates from the inner jet/core region.

Abstract

We have carried out a Chandra X-ray and multi-frequency radio VLBA study of the AGN TXS 0128+554, which is associated with the Fermi gamma-ray source 4FGL J0131.2+5547. The AGN is unresolved in a target 19.3 ks Chandra image, and its spectrum is well fit by a simple absorbed power law model, with no distinguishable spectral features. Its relatively soft X-ray spectrum compared to other CSOs may be indicative of a thermal emission component, for which we were able to obtain an upper temperature limit of kT = 0.08 keV. The compact radio morphology and measured advance speed of 0.32c +- 0.07c indicate a kinematic age of only 82 y +- 17 y, placing TXS 0128+554 among the youngest members of the compact symmetric object (CSO) class. The lack of compact, inverted spectrum hotspots and an emission gap between the bright inner jet and outer radio lobe structure indicate that the jets have undergone episodic activity, and were re-launched a decade ago. The predicted gamma-ray emission from the lobes, based on an inverse Compton-emitting cocoon model, is three orders of magnitude below the observed Fermi LAT flux. A comparison to other Fermi-detected and non-Fermi detected CSOs with redshift z<0.1 indicates that the gamma-ray emission likely originates in the inner jet/core region, and that nearby, recently launched AGN jets are primary candidates for detection by the Fermi LAT instrument.