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Paper: A Source Detection Method for ROSAT/PSPC X-Ray Images based on Wavelet Transforms
Volume: 101, Astronomical Data Analysis Software and Systems V
Page: 143
Authors: Damiani, F.; Maggio, A.; Micela, G.; Sciortino, S.
Abstract: We have developed a method based on wavelet transforms (WT) to detect sources in ROSAT PSPC X-ray images. The WT, evaluated at a set of scale parameters a, detects efficiently both point-like and extended sources. This method is especially suitable when the PSF width changes strongly across the field of view as in PSPC images. The reliability of the algorithm is ensured even in the presence of strong background gradients (detector ribs) through the use of exposure maps. The WT, computed at a scale a, is mostly sensitive to structures of size d ~ a, estimating source extent, while the height of a WT maximum gives a measure of source counts. The WT probability distribution of the background has been computed through extensive simulations, in the low-background limit and analytically in the high-background limit, to set significance thresholds for candidate sources (i.e., local WT maxima). Realistic simulations of PSPC images, containing both pure background and background plus sources, assess the frequency of spurious detections as a function of detection threshold, and the algorithm sensitivity, respectively. The algorithm may also consistently yield upper limits to the X-ray count rate of undetected objects.
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