Use the mouse to draw a region around the source of interest; all the photons within this region will be integrated to form the source spectrum. A default circular region is usually shown on the image, centered on the catalogued RA and Dec position of the source, but you may want to adjust the diameter and/or center of the circle using the mouse. Click the 'Save...' button on the 'Edit Region' window when you are finished.

In order to accurately position the regions it may be helpful to use the right mouse button to zoom in on the source and/or to adjust the brightness and contrast of the image Use the control panel on the 'Edit Region' window to set which of these functions you want the right mouse button to control.

More complicated source regions may be selected by using multiple region shapes and/or by using rectangular, elliptical, or polygon-shaped regions. You can also exclude areas within other regions, for example, to define an annular region. The excluded regions are drawn in red (by default) and are preceded by a minus sign in the output ASCII region file. More complete instructions on defining regions are available in the region help file.