We compare images of 4 flares at 3 different locations on the Sun using both SXI and RHESSI. We chose SXI images that employ the thin Be filter for the best spectral match between SXI and RHESSI; RHESSI images are in the 3-12 keV energy band. (Note that the open filter SXI images yield the same results, but we chose the Be filter images for the closest possible comparison.)

To compare the flares, we overlaid SXI images with RHESSI contours; the images in the links below are arrayed as follows:

SXI image, thin Be filter RHESSI image, 3-12 keV energy band, 30-second time integration centered at time of SXI image
SXI image overlaid with RHESSI contours @ 30%, 50%, 70%, 90% SXI image shifted MxN pixels to best match RHESSI image, overlaid with RHESSI contours (NOT shifted)

Based on information in the FITS header, the SXI images are rotated so that solar North points upwards and the E-W/N-S axes are aligned with the X-Y axes. This allows us to directly compare them to the RHESSI images.

The flares we compared are as follows:

Date
Time (UT)
X-Ray Class
 BeginMaxEnd
24-JAN-03
03:1203:2703:40
M1.9
1-FEB-03
08:4809:0509:38
M1.2
1-FEB-03
19:3219:5420:10
C9.9
6-FEB-03
03:3003:4904:01
M1.2

Click on the date of the flare (above) to see the SXI/RHESSI comparison images.

It is readily apparent that the SXI images are off from the RHESSI images by ~20 arcseconds in both X and Y (after rotation of SXI images). RHESSI has very accurate pointing based on redundant solar sensors, hence this indicates a pointing error in SXI. Since the 4 flares are at 3 different locations on the Sun, all of which lead to a similar shift, this implies the discrepancy is real and not an artifact of rotating the SXI images, else the shift would be position-dependent (which it is not).

Each SXI images required a shift of 3-5 SXI pixels down and 3-5 SXI pixels east (left); as each SXI pixels is 5x5 arcseconds, this implies an absolute pointing error of ~20 arcseconds north and ~20 arcseconds west, with an uncertainty in the error of ~5 arcseconds (1 SXI pixel) in each direction.