Multicolor Photometry of the 2001 Superoutburst of WZ Sagittae

We present the results of U‐band and multicolor photometry during the 2001 superoutburst of WZ Sge. Our 10 nights of U‐band photometry span the time interval from HJD 2,452,118 to 2,452,197, while our multicolor observations range from HJD 2,452,115 to 2,452,197. The U‐band light curves are generally in agreement with other data sets obtained during the superoutburst, showing highly modulated light early on, rebrightenings, and superhumps of similar shape and period (except during the rebrightening peak). One of our multicolor data sets fortuitously covers the first rebrightening and allows determination of the accretion disk color temperature before, during, and after the event. It is seen that the rebrightening is a change from a neutral disk (T∼7000 K) to an ionized disk (T∼10,000 K) and back again. We develop a simple limit cycle model for this behavior that approximately predicts the semiperiodic timescale observed for the rebrightenings. We discuss our results in relation to accretion disk structure during superoutburst.