The Brera Multi-scale Wavelet (BMW) ROSAT HRI source catalog. II: application to the HRI and first results

摘要

The wavelet detection algorithm (WDA) described in the accompanying paper byLazzati et al. is made suited for a fast and efficient analysis of images takenwith the High Resolution Imager (HRI) instrument on board the ROSAT satellite.An extensive testing is carried out on the detection pipeline: HRI fields withdifferent exposure times are simulated and analysed in the same fashion as thereal data. Positions are recovered with few arcsecond errors, whereas fluxesare within a factor of two from their input values in more than 90% of thecases in the deepest images. At variance with the ``sliding-box'' detectionalgorithms, the WDA provides also a reliable description of the sourceextension, allowing for a complete search of e.g. supernova remnant or clusterof galaxies in the HRI fields. A completeness analysis on simulated fieldsshows that for the deepest exposures considered (~120 ks) a limiting flux of~3x10^{-15} erg/cm2/s can be reached over the entire field of view. We testthe algorithm on real HRI fields selected for their crowding and/or presence ofextended or bright sources (e.g. cluster of galaxies and of stars, supernovaremnants). We show that our algorithm compares favorably with other X-raydetection algorithms such as XIMAGE and EXSAS. A complete catalog will resultfrom our analysis: it will consist of the Brera Multi-scale Wavelet BrightSource Catalog (BMW-BSC) with sources detected with a significance >4.5 sigmaand of the Faint Source Catalog (BMW-FSC) with sources at >3.5 sigma. Aconservative estimate based on the extragalactic log(N)-log(S) indicates thatat least 16000 sources will be revealed in the complete analysis of the wholeHRI dataset.