The La Silla QUEST Optical Variability Survey: Optical Cross-Matches to Chandra and XMM Source Catalogs

The La Silla QUEST (LSQ) supernova survey ran for 6 years on the ESO 1m Schmidt telescope at La Silla Chile, using a large CCD array to replace the photographic plate of the Schmidt. The survey imaged ~1000 degrees twice per night using a single broad V band filter, covering a total area of ~25,000 square degrees from declination ~ -50 to +20 degrees. The survey magnitude limit is V~21 in a single 60 second exposure, with an average of ~200 visits for any given patch of sky and over one thousand square degrees of sky covered by more than 1000 visits. This strict (rolling) survey cadence provides good logarithmic time coverage on timescales from ~30 minutes to ~years, enabling a wide range of variability science. Systematic photometric errors from the current differential photometry pipeline are at the 5-10 mmag level for bright point sources on a good night, with further improvements expected. Here we report on preliminary results from cross-matching La Silla QUEST to the Chandra and XMM source catalogs and characterizing the lightcurves of the matches.