An improved time delay from VLA and ATCA monitoring of the gravitational lens system PKS 1830-211

TL;DR

This study measures a more precise time delay of 25.3 days in the gravitational lens system PKS 1830-211 using VLA and ATCA data, revealing flux ratio variations likely caused by millilensing, and discusses polarization properties and lensing effects.

Contribution

The paper provides an improved measurement of the time delay in PKS 1830-211 with reduced uncertainty and analyzes flux ratio variations and polarization effects due to lensing phenomena.

Findings

Measured time delay of 25.3 +/- 2.0 days with higher precision.

Detected long-term flux ratio variations attributed to millilensing.

Identified polarization and morphology features influenced by lensing effects.

Abstract

We have measured a time delay of 25.3 +/- 2.0 d (1-sigma confidence) in the Einstein ring gravitational lens system PKS 1830-211 from an analysis of archival VLA and ATCA monitoring data observed between 1997 and 2004. A small portion of the ATCA data was previously used to determine a time delay and our result is consistent with the previous value, but with an uncertainty that is smaller by more than a factor of two. The long time-baseline of the monitoring reveals that the flux density ratio is smoothly varying on a time-scale of years, an effect which we attribute to millilensing by massive objects (>>1 M_sun) in the lensing galaxy. Image A is unpolarized in the VLA monitoring, but VLBI observations show that this is partly due to beam dilution by an unpolarized counter-jet that is only present in that image. Based on the identification of this feature as a counter-jet, we conclude that its unexpected prominence in image A is a consequence of lensing and that more detailed modelling is required in order to reconcile the VLBI morphology of each image.