New Estimates of Time Delays in the Gravitationally Lensed System PG1115+080

TL;DR

This study estimates time delays in the gravitational lens system PG1115+080 using long-term optical data, applying the MCCF method, and compares results with previous studies, revealing some discrepancies and consistencies with lens models.

Contribution

The paper provides new estimates of time delays in PG1115+080 using the MCCF method and compares them with previous results, highlighting differences and agreements.

Findings

Estimated time delays: τ_BC=22+2-3 days, τ_AC=12+2-1 days, τ_BA=10+2-3 days.

The ratio τ_AC/τ_BA is approximately 1.2, close to some lens model predictions.

Results are consistent with some previous studies but differ from others.

Abstract

We analyze all publicly available long-term optical observations of the gravitationally lensed quasar PG1115+080 for the purpose of estimating time delays between its four components. In particular, the light curves of PG1115+080 components obtained in 2001-2006 at Maidanak observatory (Uzbekistan) (Tsvetkova et al 2010} are considered. We find that the linear trend is observed in 2006 in light curves of all four components with fast variations only in the A1 and C components that can be due to microlensing and observational errors. Application of the MCCF method (Oknyansky 1993) to the photometric data obtained in 2004-2005 gives values of time delays $\tau_{BC} = 22^{+2}_{-3}$, $\tau_{AC} = 12^{+2}_{-1}$ and $\tau_{BA} = 10^{+2}_{-3}$ days, which are in agreement with the results received earlier by Schechter and Barkana for 1995-1996 light curves with two different methods of statistic analysis. However, our estimates of $\tau_{BA}$ and $\tau_{BC}$ differ from the values received by the group of Vakulik based on the same Maidanak data (Vakulik et al 2009). The ratio $\tau_{AC}/\tau_{BA}$ is equal to $\sim 1.2$ that is close to the value, received by Barkana ($\sim 1.13$) and predicted by lens models ($\sim1.4$), unlike the values received by Schechter ($\sim 0.7$) and Vakulik ($\sim 2.7$).