PG 1115+080: variations of the A2/A1 flux ratio and new values of the time delays

TL;DR

This study presents new measurements of flux ratios and time delays in the gravitational lens PG 1115+080, revealing microlensing effects and refining the Hubble constant estimates through detailed multicolor observations.

Contribution

It provides updated time delays and flux ratio variations in PG 1115+080, highlighting microlensing effects and implications for cosmological parameters.

Findings

New time delays: B-C 16.4 days, (A1+A2)-C 12 days.

Flux ratio A2/A1 increased to 0.85 in 2006.

Evidence of microlensing affecting images A1 and A2.

Abstract

We report the results of our multicolor observations of PG 1115+080 with the 1.5-m telescope of the Maidanak Observatory (Uzbekistan, Central Asia) in 2001-2006. Monitoring data in filter R spanning the 2004, 2005 and 2006 seasons (76 data points) demonstrate distinct brightness variations of the source quasar with the total amplitude of almost 0.4 mag. Our R light curves have shown image C leading B by 16.4d and image (A1+A2) by 12d that is inconsistent with the previous estimates obtained by Schechter et al. in 1997 - 24.7d between B and C and 9.4d between (A1+A2) and C. The new values of time delays in PG 1115+080 must result in larger values for the Hubble constant, thus reducing difference between its estimates taken from the gravitational lenses and with other methods. Also, we analyzed variability of the A2/A1 flux ratio, as well as color changes in the archetypal "fold" lens PG 1115+080. We found the A1/A2 flux ratio to grow during 2001-2006 and to be larger at longer wavelengths. In particular, the A2/A1 flux ratio reached 0.85 in filter I in 2006. We also present evidence that both the A1 and A2 images might have undergone microlensing during 2001-2006, with the descending phase for A1 and initial phase for A2. We find that the A2/A1 flux ratio anomaly in PG 1115 can be well explained both by microlensing and by finite distance of the source quasar from the caustic fold.