Other sources in the field not under this rib will in general be occulted by some part of the PSPC window support structure for only part of the observation. The wobble is much less noticeable in HRI images because the HRI does not have any support structure. Images are stored based on the RA of the center of the field of view. Directly below the images directory are subdirectories of right ascension in hours. There are 3 versions of each of these text files which only differ in the type of special characters used to indicate the end of each line of text.
All images use a sky coordinate system in which North is to the top and East to the left.
The units in the images are counts per detector pixel. The units in the uncompressed exposure maps are seconds of time. The FITS files may be displayed using any data display package which accepts FITS data. To save space, these maps have been compressed using the Unix compress facility. These GIF images are provided to allow a quick look at the data.