On the Doppler boosting in the compact radio jet of the distant blazar J1026+2542 at z=5.3

TL;DR

This paper investigates the relativistic jet properties of the distant blazar J1026+2542 at redshift 5.3, analyzing VLBI data to assess Doppler boosting and jet orientation, contributing to understanding high-redshift AGN physics.

Contribution

It provides the first estimate of the brightness temperature and jet orientation of a high-redshift blazar, challenging assumptions about Doppler boosting at such distances.

Findings

No strong evidence for Doppler boosting in J1026+2542.

Jet viewing angle is at least ~20 degrees.

Future multi-epoch VLBI observations can determine jet Lorentz factor and viewing angle.

Abstract

Based on its broad-band spectral energy distribution, and the X-ray spectrum in particular, the radio-loud active galactic nucleus (AGN) SDSS J102623.61+254259.5 (J1026+2542) has recently been classified as a blazar. The extremely high redshift of the source, z=5.3, makes it one of the most distant and most luminous radio-loud AGN known to date. From published 5-GHz very long baseline interferometry (VLBI) imaging data obtained in 2006, the source has a typical blazar appearance on mas scales, with a prominent one-sided jet extending to ~20 mas. We estimate the brightness temperature of J1026+2542 and find no strong evidence for Doppler boosting. The jet viewing angle is possibly at least ~20 deg. The bulk Lorentz factor and the viewing angle of the jet could reliably be determined in the near future from multi-epoch VLBI observations.