This returns an event list of the background data, as a generic task.
For EPIC this CAL routine should be used only in cases where the background estimated from source-free regions of an exposure cannot be used (e.g. very extended sources, small windows extent). The background is dependent on a large number of factors, especially user-defined data selections, such as energy range, event selections etc..
Since launch it has been noted that the background depends to a significant degree on the effect of soft proton flares. These flares are variable in intensity and spectrum, so a generic background file is unlikely to have a high fidelity reproduction of actual background experienced.
The approach suggested ad interim is to have large event files
extracted from quiet intervals.