Multiple Concentric Annuli for Characterizing Spatially Nonuniform Backgrounds

A method is presented for estimating the background at a given location on a sky map by interpolating the estimated background from a set of concentric annuli that surround this location. If the background is nonuniform but smoothly varying, this method provides a more accurate (although less precise) estimate than can be obtained with a single annulus. Several applications of multiannulus background estimation are discussed, including direct testing for point sources in the presence of a nonuniform background, the generation of surrogate maps for characterizing false alarm rates, and precise testing of the null hypothesis that the background is uniform. copyright copyright 1999. The American Astronomical Society