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Purpose: Uses the output of OVERLAP (overlap_n.out for PSPC data for band n; overlap.out for HRI data) and exposure arrays to create offset count maps for the individual observations. When cast with the count, background, and exposure maps, the offset count maps will produce a relatively uniform zero level across the field. Again, while the zero level may not be at true zero, the relative variations in the final image will be more reliable.
1) Other fixed input - after the band has been selected, overlap_n.out output from the OVERLAP. This file contains the directory string, central coordinates, and scale factor for the offset for the observation analyzed by OVERLAP. After the mask has been selected, the program reads in the appropriate cast exposure and mask for each observation.
1) Coordinate control - determines the coordinate system for the mosaic image. 1 for ecliptic, 2 for equatorial, or 3 for galactic coordinates.
2) Central coordinates - the center of the mosaic image in decimal degrees in the coordinate system selected in 1).
3) Scale factor for mosaic - arc minutes per pixel for the mosaic.
4) Radius limit - the radius of the region in the observation, in arc minutes, to be cast into the mosaic (applied to the sky image rather than the detector image). A limit of 53' for PSPC data serves reasonably well to exclude the worst problems caused by the large point response function at large off-axis angles.
5) Band to be cast - the program will cast only one band at a time.
6) Mask file name for masking of the data - the data will be masked using files with the input file name. The mask files must be in the same directories as the data files. If no additional masking is desired, enter ``none''.
7) Add to an existing array - data can be added to an existing array.
Fits file off_n.fits (off.fits for HRI data) containing the cast offset counts.