Impact of Microlensing on Observational Strategies for Gravitational
  Time Delay Measurements
  Microlensing not only brings extra magnification lightcurves on top of the
intrinsic ones but also shifts them in time domain, making the actual
time-delays between images of strongly lensed active galactic nucleus change on
the $\sim$ day(s) light-crossing time scale of the emission region. The
microlensing-induced time-delays would bias strong lens time-delay cosmography
if uncounted. However, due to the uncertainties of the disk size and the disk
model, the impact is hard to accurately estimate. In this work, we study how to
reduce the bias with designed observation strategy based on a standard disk
model. We find long time monitoring of the images could alleviate the impact
since it averages the microlensing time-lag maps due to the peculia motion of
the source relative to the lens galaxy. In addition, images in bluer bands
correspond to smaller disk sizes and therefore benefit time-delay measurements
as well. We conduct a simulation based on a PG 1115+080-like lensed quasar. The
results show the time-delay dispersions caused by microlensing can be reduced
by $\sim40\%$ with 20-year lightcurves while u band relative to r band reduces
$\sim75\%$ of the dispersions. Nevertheless, such an effect can not be totally
eliminated in any cases. Further studies are still needed to appropriately
incorporate it in inferring an accurate Hubble constant.
