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

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 ($\sim 2.7$).