Flux and color variations of the doubly imaged quasar UM673

TL;DR

This study monitored flux and color changes in the gravitationally lensed quasar UM673 over four seasons, revealing significant brightness variations and smaller color changes than previously observed, using multi-band photometry.

Contribution

It provides detailed multi-epoch, multi-band photometric analysis of UM673, including separation of the lensing galaxy's contribution, which was not extensively done before.

Findings

Significant flux decrease and increase in the brightest component over seasons.

Smaller color variations compared to previous studies.

Separation of lensing galaxy contribution from the lensed components.

Abstract

With the aim of characterizing the flux and color variations of the multiple components of the gravitationally lensed quasar UM673 as a function of time, we have performed multi-epoch and multi-band photometric observations with the Danish 1.54m telescope at the La Silla Observatory. The observations were carried out in the VRi spectral bands during four seasons (2008--2011). We reduced the data using the PSF (Point Spread Function) photometric technique as well as aperture photometry. Our results show for the brightest lensed component some significant decrease in flux between the first two seasons (+0.09/+0.11/+0.05 mag) and a subsequent increase during the following ones (-0.11/-0.11/-0.10 mag) in the V/R/i spectral bands, respectively. Comparing our results with previous studies, we find smaller color variations between these seasons as compared with previous ones. We also separate the contribution of the lensing galaxy from that of the fainter and close lensed component.