The task espfilt applies one of two user-chosen methods for filtering an XMM-Newton Event List (MOS or PN) of cosmic soft proton events. The methods both utilize corner (unexposed, outside of FOV) sections of the CCDs. Both methods extract a lightcurve from both the FOV and the corners.
The histogram method fits a roughly Gaussian to a histogram of
the FOV lightcurve values. The peak of that Gaussian is taken as the
nominal count rate. A user specified number of 
around the
peak (default:2.5) are taken to be “flare-free” The program then
creates a GTI file for those “flare-free” time intervals and then
creates a filtered event file using that GTI.
The ratio method takes the ratio of counts per pixel of an annulus near the edge of the FOV (and away from any bright central source) to that of the unexposed corners. The time intervals with a ratio below a user-defined threshold (default: 1.2) are taken to be “flare-free”. The program creates a GTI for the “flare-free” time intervals and then creates a filtered event file using that GTI.
In both methods, a new filtered event list, lightcurves of the FOV and corners, GTI FITS files, filtered images and a QDP plot of the lightcurves are created (histo method ONLY).
