Revisiting the relativistic ejection event in XTE J1550-564 during the 1998 outburst

TL;DR

This paper analyzes the 1998 outburst of XTE J1550-564, focusing on relativistic jet ejections, their velocities, and spectral properties, providing insights into jet dynamics and source distance.

Contribution

It offers a detailed reanalysis of jet ejection events, velocities, and spectral characteristics during the 1998 outburst, refining previous understanding.

Findings

Ejection velocity at least 1.3c, possibly up to 1.9c

True velocity inferred to be >0.8c after relativistic correction

Radio flux peaks simultaneously with the outburst

Abstract

We revisit the discovery outburst of the X-ray transient XTE J1550-564 during which relativistic jets were observed in 1998 September, and review the radio images obtained with the Australian Long Baseline Array, and lightcurves obtained with the Molonglo Observatory Synthesis Telescope and the Australia Telescope Compact Array. Based on HI spectra, we constrain the source distance to between 3.3 and 4.9 kpc. The radio images, taken some two days apart, show the evolution of an ejection event. The apparent separation velocity of the two outermost ejecta is at least 1.3c and may be as large as 1.9c; when relativistic effects are taken into account, the inferred true velocity is >0.8c. The flux densities appear to peak simultaneously during the outburst, with a rather flat (although still optically thin) spectral index of -0.2.