|ROSAT Home Page||ROSAT
Purpose: To identify point sources in the field covered by a single observation and to create a point-source mask for that field. DETECT uses a sliding box algorithm with the slight improvement that the box is a circle where the radius is a function of off-axis angle. The source-identification threshold can be set for both count rate and significance, both at the same time if desired. The program sets a ``source'' radius at the 90% encircled energy radius and the background annulus at 2.5 times the 90% encircled energy radius. For a sparse image, if fewer than four counts are found in the background annulus the average background for the observation is used. The significance is determined using Poisson statistics but does not consider the number of trials. This program is not meant to supercede other source detection algorithms in other analysis packages, only to be consistent with the files and processing produced and used in the associated programs.
1) Observation data set fits files - none
2) Other fixed input - after the band has been selected, the program reads in the appropriate count image(s) and exposure map(s).
1) Band range - the range of bands to be analyzed for point sources. The most useful ranges are ``1 2'' (or ``8 2'' where the R1L band has been used) for a 1/4 keV band mask, ``4 7'' for a hard band mask (0.5 - 2.0 keV). ``0 0'' for the HRI.
2) Statistical significance and count-rate threshold - statistical significance: either the Poisson (i.e., ) probability or the value in sigmas (allowed values: 1., 2., 2.5, 3., 3.5, 4., 4.5, 5., 5.5). Count-rate threshold: units of counts s (may be set to zero).
File diag_n.dat where n is the band (i.e., mask_5.fits) or band range (i.e., mask_47.fits) containing information on the detected sources: source number, X pixel for source, Y pixel for source, source count rate in counts s , and source significance.
Fits file mask_n.fits (use of ``n'' as above; mask.fits for the HRI) of the point-source mask. Masked regions (a radius of 1.5 times the 90% encircled energy radius) are set to 0.0, accepted regions are set to 1.0. Regions where the exposure is zero are set to zero.