COSMOGRAIL XVII: Time delays for the quadruply imaged quasar PG 1115+080

TL;DR

This paper presents precise time-delay measurements for the quadruply imaged quasar PG 1115+080, using extensive observational data and analysis that accounts for potential microlensing bias, improving the accuracy of cosmological inferences.

Contribution

The study provides the most precise time-delay estimates for PG 1115+080 by combining new and existing data, and investigates microlensing effects, which were previously not directly addressed.

Findings

No significant microlensing time delay detected.

Achieved the most precise time-delay measurements to date.

Results are consistent with previous studies.

Abstract

We present time-delay estimates for the quadruply imaged quasar PG 1115+080. Our resuls are based on almost daily observations for seven months at the ESO MPIA 2.2m telescope at La Silla Observatory, reaching a signal-to-noise ratio of about 1000 per quasar image. In addition, we re-analyse existing light curves from the literature that we complete with an additional three seasons of monitoring with the Mercator telescope at La Palma Observatory. When exploring the possible source of bias we consider the so-called microlensing time delay, a potential source of systematic error so far never directly accounted for in previous time-delay publications. In fifteen years of data on PG 1115+080, we find no strong evidence of microlensing time delay. Therefore not accounting for this effect, our time-delay estimates on the individual data sets are in good agreement with each other and with the literature. Combining the data sets, we obtain the most precise time-delay estimates to date on PG 1115+080, with Dt(AB) = 8.3+1.5-1.6 days (18.7% precision), Dt(AC) = 9.9+1.1-1.1 days (11.1%) and Dt(BC) = 18.8+1.6-1.6 days (8.5%). Turning these time delays into cosmological constraints is done in a companion paper that makes use of ground-based Adaptive Optics (AO) with the Keck telescope.