COSMOGRAIL XIX: Time delays in 18 strongly lensed quasars from 15 years
  of optical monitoring
  We present the results of 15 years of monitoring lensed quasars, which was
conducted by the COSMOGRAIL programme at the Leonhard Euler 1.2m Swiss
Telescope. The decade-long light curves of 23 lensed systems are presented for
the first time. We complement our data set with other monitoring data available
in the literature to measure the time delays in 18 systems, among which nine
reach a relative precision better than 15% for at least one time delay. To
achieve this, we developed an automated version of the curve-shifting toolbox
PyCS to ensure robust estimation of the time delay in the presence of
microlensing, while accounting for the errors due to the imperfect
representation of microlensing. We also re-analysed the previously published
time delays of RX J1131$-$1231 and HE 0435$-$1223, by adding six and two new
seasons of monitoring, respectively, and confirming the previous time-delay
measurements. When the time delay measurement is possible, we corrected the
light curves of the lensed images from their time delay and present the
difference curves to highlight the microlensing signal contained in the data.
To date, this is the largest sample of decade-long lens monitoring data, which
is useful to measure $H_0$ and the size of quasar accretion discs with
microlensing as well as to study quasar variability.
