Subject: Imaging with RHESSI Grids 1 and 2

Imaging with grids 1 and 2 is now supported by the latest version of the
subcollimator response table (SRT_20020716.dat).  Their FWHM resolutions
are 2.26 and 3.92 arcseconds respectively.  Parameters for grids 3-9 are
the same as before.  Events that may benefit from the higher resolution
include 25 March at 20:07 and 20 April at 23:26.  

As mentioned earlier, there are some caveats that should be kept in mind
when using the higher resolution grids:

* Since coarser grids can be processed faster than finer grids,
processing times may be longer if grids 1 and/or 2 are included.

* Since a given grid only modulates source structure that is finer than
about the grid resolution, some sources may not have fine enough spatial
structure to benefit from the use of grids 1 or 2.  Their inclusion in
such cases will not improve and may in fact slightly degrade the
mapping.  One option is to make preliminary maps first using grids 3 and
higher to see if there are any apparently unresolved sources.

* Since February, the grid 2 energy threshold has been set to ~20 keV.

* Since artifacts may result if the pixel size is chosen to be larger
than about 1/2 of the subcollimator FWHM, the pixel size should be
chosen to be no larger than 1 or 2 arcseconds respectively for grids 1
or 2.

Please let me know if you encounter any problems.

Good luck!