1999ApJ...524..423C

The wavelet detection algorithm (WDA) described in the accompanying paper by Lazzati et al. is suited to a fast and efficient analysis of images taken with the High-Resolution Imager (HRI) instrument on board the ROSAT satellite. An extensive testing is carried out on the detection pipeline: HRI fields with different exposure times are simulated and analyzed in the same fashion as the real data. Positions are recovered with errors of a few arcseconds, whereas fluxes are within a factor of 2 from their input values in more than 90% of the cases in the deepest images. Unlike the ``sliding-box'' detection algorithms, the WDA also provides a reliable description of the source extension, allowing for a complete search of, e.g., supernova remnants or clusters of galaxies in the HRI fields. A completeness analysis on simulated fields shows that for the deepest exposures considered (∼120 ks) a limiting flux of ∼3x10^–15 ergs.s^–1.cm^–2 can be reached over the entire field of view. We test the algorithm on real HRI fields selected for their crowding and/or the presence of extended or bright sources (e.g., clusters of galaxies and stars, supernova remnants). We show that our algorithm compares favorably with other X-ray detection algorithms, such as XIMAGE and EXSAS. Analysis with the WDA of the large set of HRI data will allow us to survey ∼400 deg² down to a limiting flux of ∼10^–13 ergs.s^–1.cm^–2, and ∼0.3 deg² down to ∼3x10^–15 ergs.s^–1.cm^–2. A complete catalog will result from our analysis, consisting of the Brera Multiscale Wavelet Bright Source Catalog (BMW-BSC), with sources detected with a significance of ≳4.5 σ, and the Faint Source Catalog (BMW-FSC), with sources at ≳3.5 σ. A conservative estimate based on the extragalactic log N-log S indicates that at least 16,000 sources will be revealed in the complete analysis of the entire HRI data set.