First generate a vignetting mask appropriate for an energy of 1.0 keV (central energy in the ROSAT PSPC) for the image xdata$rp110590.qp:
input file: xdata$snr.qp
output file snr_vig.pl
xr> xspatial xs> makevig "xdata$rp110590.qp[bl=30]" arlac " " 1. # generates # output mask arlac_vig.pl at energy 1.0 keVNow apply vignetting correction to the image generating a vignetting corrected output image and error array:
input files: xdata$snr.qp, snr_vig.pl
output files: vigsnr.imh, vigsnr_err.imh
xs> ximage # load package xi> vigdata # vignetting correction Input image file : xdata$110590.qp[bl=30] # From the original QPOE file Output vignetted image file : arlac # give *.imh extension! Vignetting corrections mask : arlac_vig.pl # All extensions explicit fraction of image which is non-vign bkgd (x.xx format): 0.05 # 5% of the image counts are non-vignetted background # and will not be corrected # The format is important Input error image file : xdata$rp110590.qp[bl=30] # The error is taken as # square root of n from the original data Output vignetted error file : <cr> # =vigsnr_err.imh
This method of applying vignetting assumes that background counts dominate the image. In the ROSAT PSPC the non-vignetted (charged particle) background is a minor contribution to the background with a typical rate of cts s-1arcmin-2keV-1(see Plucinsky et al., Ap.J., 418, 519, 1993 for a detailed discussion).