This section will deal with obtaining photons within specified regions of an image. Available regions are:
Annulus Box Circle Ellipse Field -- entire field Irregular region based on intensity of map... i.e. region defined by contour levels. Pie -- angular wedge Point Polygon Rotbox -- rotated box
for more details type:
cl> help regions
The imcnts task in the xray-spatial package sums the source and background counts in specified regions, and subtracts one from the other properly normalized. The results are saved in a table file, which can be read, printed or converted into an ascii file using the ttools.
The sample data file, xdata$rp110590.qp, contains a point source whose position is at x = 6930, y = 9390. The counts will be taken within a circle of 240 pixel radius (2' in the ROSAT PSPC. This is the recommended circle size for a PSPC point source which is not too far off axis). The examples requiring an extended source will use the data file, xdata$snr.qp, containing Einstein IPC data. Counts will be obtained in a box of 208 266 pixels, with exclusion of the point source at 503,513.