The SXT X-ray effective area varies across the 
arcmin
field-of-view. The shape of the vignette function can be examined with
the IDL program HELP_VIGNETTE. At 21 arcmin from the optical
axis, the low-energy response (
keV) falls to approximately 75%
and the high-energy response (2.98 keV) falls to approximately
50% of the on-axis value (see the Instrument Guide for more
details). Because of this, some care should be taken when, for example,
making temperature analyses with thin and thick filters of flares that
occur near the solar limb.
There are no fully approved routines to remove or correct for the SXT vignette function. There are, however, two preliminary routines. SXT_VIGNETTE will compute the vignette function as it is currently understood. The form and parameters of the shape may be changed as additional data and analysis results become available. The routine SXT_OFF_AXIS will correct for the vignette function by calling SXT_VIGNETTE. Users are warned that these routines are preliminary and may not be the most appropriate technique to use, depending on the scientific application.