  We present new brightness monitoring observations of the 4 components of
gravitationally lensed system Q2237+0305, which show detection of an intrinsic
quasar brightness fluctuation at a time of subdued microlensing activity,
between June 27 and October 12, 2003. These data were used to determine the
time delays between the arrivals of the four images. The measured delays are
-6, 35, and 2 hours for images B, C and D relative to A, respectively, so they
confirm that the long history of brightness monitoring has produced significant
detection of microlensing. However the error bars associated with the delays,
of order 2 days, are too large to discriminate between competing macro-imaging
models. Moreover, our simulations show that for the amplitude of this intrinsic
fluctuation and for photometric errors intrinsic to optical monitoring from our
1.5-m telescope or from the OGLE monitoring, a daily sampled brightness record
cannot produce reliable lags for model discrimination. We use our simulations
to devise a strategy for future delay determination with optical data.
Nevertheless, we regard these first estimates to be significant, since they are
the first direct measurements of time delays made for this system from
ground-based observations in the visual wavelengths. Our results provide the
most convincing confirmation of the gravitational-lens nature of Q2237+0305,
and give observational justification to the extensive literature which
attributes the quasar's previously observed brightness fluctuations to
microlensing.
