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