The proper motion and changing jet morphology of Cygnus X-3

TL;DR

This study analyzes 25 years of radio observations of Cygnus X-3 to determine its proper motion, jet morphology, and velocity, revealing jet precession and constraining the system's space velocity.

Contribution

It provides the first long-term proper motion measurement of Cygnus X-3 and demonstrates jet precession using archival VLBI data.

Findings

Proper motion constrains system velocity to at least 9 km/s

Jet orientation varies over time, indicating precession

Jets are aligned close to the line of sight

Abstract

We present analysis of 25 years' worth of archival VLA, VLBA and EVN observations of the X-ray binary Cygnus X-3. From this, we deduce the source proper motion, allowing us to predict the location of the central binary system at any given time. However, the line of sight is too scatter-broadened for us to measure a parallactic distance to the source. The measured proper motion allows us to constrain the three-dimensional space velocity of the system, implying a minimum peculiar velocity of 9 km/s. Reinterpreting VLBI images from the literature using accurate core positions shows the jet orientation to vary with time, implying that the jets are oriented close to the line of sight and are likely to be precessing.