COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses XII.
  Time delays of the doubly lensed quasars SDSS J1206+4332 and HS 2209+1914
  Aims. Within the framework of the COSMOGRAIL collaboration we present 7- and
8.5-year-long light curves and time-delay estimates for two gravitationally
lensed quasars: SDSS J1206+4332 and HS 2209+1914. Methods. We monitored these
doubly lensed quasars in the R-band using four telescopes: the Mercator,
Maidanak, Himalayan Chandra, and Euler Telescopes, together spanning a period
of 7 to 8.5 observing seasons from mid-2004 to mid-2011. The photometry of the
quasar images was obtained through simultaneous deconvolution of these data.
The time delays were determined from these resulting light curves using four
very different techniques: a dispersion method, a spline fit, a regression
difference technique, and a numerical model fit. This minimizes the bias that
might be introduced by the use of a single method. Results. The time delay for
SDSS J1206+4332 is Delta_t AB = 111.3 +/- 3 days with A leading B, confirming a
previously published result within the error bars. For HS 2209+1914 we present
a new time delay of Delta_t BA = 20.0 +/- 5 days with B leading A. Conclusions.
The combination of data from up to four telescopes have led to well-sampled and
nearly 9-season-long light curves, which were necessary to obtain these
results, especially for the compact doubly lensed quasar HS 2209+1914.
