Dear RHESSI software users,

We've changed the default values for some control parameters in
the RHESSI and OSPEX objects.  The purpose of these changes is to
make the defaults the parameter values that work best in most common
situations.  Of course you should continue to change these and other
parameters for particular cases.  The names of the parameters that
were changed and a short explanation are listed below.

In the RHESSI spectrum object:

1. sp_energy_binning
The default energy binning code has been changed from 7 to 14.
14 has 77 bins ranging from 3 to 250 keV (1 keV wide bins at low
energies and wider bins at higher energies) and is good for analyzing
hard x-ray flares.  You may also want to consider binning code 22
which is similar, but has 101 bins ranging from 3 to 300 keV with
1/3 keV wide bins from 3 to 15 keV.

2.  sp_time_interval
The default time bin width is now 4 seconds.  This is more suitable
for the analysis of temporal structure. Previously it was 60 seconds.

3.  simplify
The full SRM will now be written in the FITS output file when you
write the spectrum and SRM files.   Previously it was the diagonal
SRM.  In some cases calculation of the full SRM will take longer
(if you have a large number of energy bins), but for spectral
analysis you almost always want to use the full SRM.

In the RHESSI image object:

1.  natural_weighting, uniform_weighting
The default is now natural weighting (all collimators have
equal weight).  Previously it was uniform weighting (weight
each collimator by the inverse of its FWHM).  Natural weighting
is better for extended sources and allows the finer grids to be
utilized without adding to the noise; uniform weighting provides
greater sensitivity for compact sources.  This is used only in the
back-projection and clean algorithms.

2.  use_flux_var
use_flux_var is now enabled by default.   When enabled, the software
attempts to construct a demodulated profile of the true incident
flux variation in the energy band, unmarred by grid modulation.
This can be critical for algorithms that try to minimize the
fitting statistic.

3.  use_rate
use_rate is now enabled by default.  This enables the rate-based
back projection.  This is particularly critical to set when
deadtimes become greater than 50%.  For smaller deadtimes, it has
little effect.  For dirty (back-projection) maps made with use_rate
set to 0, the true source positions may have the lowest (negative)
values in the field. Setting use_rate to 1 corrects that and the
source positions will again have the highest values and appear
brightest in the dirty map images. For the CLEAN algorithm to work,
the source positions must have the highest values.

4.  image_algorithm
The MEM VIS algorithm has been disabled.  It didn't work.
The MEM Sato algorithm is no longer an option from the hessi GUI.
You can continue to use it from the command line, but we don't
have confidence in the results.  Two new image algorithms that use
visibilities will be available soon.

5.  clean_niter
The number of iterations in the CLEAN algorithm is now 100.
Previously it was 33.

6.  clean_frac
The gain in the CLEAN algorithm is now 0.05.  Previously it was 0.10.
In each iteration of CLEAN, the clean_frac fraction of the peak
value is multiplied by the point spread function and subtracted.

We want to encourage users to explore using parameter values other
than the defaults.  In particular, users should vary their choice
of the range of collimators used (det_index_mask parameter), pixel
size (pixel_size parameter), and energy range (im_energy_binning
parameter).  And we want to remind users to exclude detector 2
when using energies below 20 keV, and to use smaller pixel size
with the finer grids.

In the OSPEX object:

1.  spex_uncert
The systematic uncertainty is now 0.02.  Previously it was 0.05.
Setting this parameter too high results in an artificially low
value for chi-squared.  You may want to set it 0.0.

Please let us know if you have any questions about this.