This task is designed to analyse a circular region within an image, specified in celestial coordinates, and calculate the upper limit at that position. It has been designed to run as quickly as possible and to that end avoids using any calibration quantities. The input image should be in sky coordinates and WCS keywords in the header are used to find the required position within the image. The task should run on any sky image regardless of the instrument.
A more flexible but slower result for XMM-Newton EPIC images, using the full XMM-Newton calibration, can be obtained from the eregionanalyse task.