Greg Dobler edited Sampling.tex  over 10 years ago

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While this quality of measurement is possible for small samples (a few tens) of lenses, the larger sample of lensed quasars lying in the LSST survey footprint will all be monitored over the course of its ten year campaign, but at lower cadence and with shorter seasons. In the simplest possible ``universal cadence'' observing strategy, we would expect the mean cadence to be around 4 days between visits, in any filter, and with some variation with time as the scheduler responds to the needs of the various science programs and the changing conditions; the gaps between observations in the same filter will tend to be longer \citep{LSSTpaper,LSSTSciBook}. The season length in this strategy is likely to be approximately 4 months (with variation among filters), in order to keep the telescope pointing at low airmass. The primary impact of the shorter season length will be to make it hard to measure time delays of more than 100 days; the LSST universal cadence time delay lens sample would be biased towards delays shorter than this.  {\bf (GGD: In the paragraph below, we aren't actually doing this testing COSMOGRAIL accuracy  in TDC though...)} The universal cadence strategy may not turn out to be optimal, and we can explore various LSST observing strategies by simulating light curves with a range of cadences and season lengths. The shorter cadences and longer seasons are closer to those obtained by COSMOGRAIL and blind analysis of those datasets will provide understanding of the accuracy available to that program as its lens sample increases. We note that only if all filters' light curves can be fitted simultaneously with a model for the multi-filter variability would the maximum, any-filter cadence be fully exploited -- but that even if this is not possible, the dithered nature of the different filters' light curves should still allow a time resolution {\it approaching} that of the any-filter cadence.  The remaining variables in the mock lightcurve generation pertain to the photometric uncertainties applied to the observed fluxes. \citet{TewesEtal2013a} provide a summary of possible sources of uncertainty and error in the photometric measurements, and we follow this in generating lightcurves with realistic uncertainties, including in the accuracy of the error reporting. The OM10 mock lens sample contains a variety of quasar image brightnesses, allowing us to investigate time delay accuracy as a function of signal to noise, or for LSST, source magnitude.