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W. Colley, R. Schild (Harvard-Smithsonian CfA)
We have re-reduced 1600 CCD images of the Twin Quasar Q0957+561, taken over 25 nights with ~4 minute time resolution. The new reduction uses HST imaging to subtract the lens galaxy accurately. This refined photometry shows variations of order a percent during the typical night. Two runs, separated by the now widely accepted ~417 day time delay allow us to shift and match trailing image B photometry with leading image A photometry to determine whether the variations are intrinsic to the quasar or caused by microlensing. Results suggest that the dominant signal is quasar intrinsic and give a refined time delay of 417.4 days. Any microlensing signal on these timescales would suggest a dark matter component in the lens galaxy which is comprised of very small (~10-5M\odot) MACHO's. However, both microlensing detection and time delay estimation are highly susceptible to diurnal windowing due to daylight, inevitable at a single observatory. We have thus initiated a new collaboration called ``QuOC Around the Clock'' in which we will observe the quasar continuously from several observatories around the globe for ten days, first in January 2000, then 417 days later in March 2001. With our refined photometric methods, we will report a time delay precise to a tenth of a day, and report significantly the presence or absence of microlensing on daily timescales.
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The author(s) of this abstract have provided an email address for comments about the abstract: wcolley@cfa.harvard.edu