Physical parameters of a relativistic jet at very high redshift: the case of the blazar J1430+4204

TL;DR

This study investigates the relativistic jet parameters of the high-redshift blazar J1430+4204 using VLBA radio observations before and after a major outburst, finding no new jet components but estimating key physical parameters.

Contribution

The paper provides the first detailed analysis of the jet physical parameters of a high-redshift blazar during an outburst using VLBA data, with no new jet features detected.

Findings

No significant new jet component detected over 569 days.

Estimated Doppler and Lorentz factors of the jet.

Jet angle to line of sight is likely small.

Abstract

Context. The high-redshift (z = 4.72) blazar J1430+4204 produced a major radio outburst in 2005. Such outbursts are usually associated with the emergence of a new component in the inner radio jet. Aims. We searched for possible changes in the radio structure on milli-arcsecond angular scales, to determine physical parameters that characterise the relativistic jet ejected from the centre of this source. Methods. We analysed 15-GHz radio interferometric images obtained with the Very Long Baseline Array (VLBA) before and after the peak of the outburst. Results. We did not identify any significant new jet component over a period of 569 days. We estimated the Doppler factor, the Lorentz factor, and the apparent transverse speed of a putative jet component using three different methods. The likely small jet angle to the line of sight and our values of the apparent transverse speed are consistent with not detecting a new jet feature.