Phil Evans spotted a subtle problem using filter intensity. Extra time is rejected at the start and end of each gti of the lightcurve used as the basis of the intensity filtering. The reason is that the lightcurve assigns a time to the center of the bin and these times are used by maketime to create the filter gtis. We used prefr=postfr=0.5 in maketime so that if bin I does not satisfy the filter and bin I+1 does then the starting time of the gti is (t(I)+t(I+1) )/2, which is correct. However, if the first or last bin of an input gti satisfies the filter then maketime just uses t(I) leading to the loss of half a bin. I've corrected this by writing a perl script called by the filter intensity command which creates a new temporary lightcurve with extra bins before and after each gti (and with rate=0). This temporary lightcurve is used as the input for maketime and ensures that no time is lost. A test is to do a filter intensity with range 0.0-* then extract a new lightcurve. The result has exactly the same gti as the pre-filtered lightcurve.
Keywords: HEAsoft, xselect