An energy filter and blocking
factor will be applied to match those of the background map.
Use the ROSAT broad band background which is a 
array file at
1/30 the *.qp file resolution, and contains data from PI bins 7--240.
input files: xdata$rp110590.qp; xdata$rp110590_bk1.imh
output file: rp90_a.imh
xr> ximages
xi> imcalc
input file ('-' for STDIN) or imcalc commands: - # Interactive mode
IMC)
IMC) rp90_a.imh = xdata$rp110590.qp[bl=30,pi=7:240] - xdata$rp110590_bkl.imh
# Select same size and channels as the background map
# and subtract the background
IMC) quit # To exit the interactive mode and imcalc
The output file is a 
array containing data in the
broad PSPC band.