Spectral analysis of RHESSI data is currently a two step process. The
spectroscopy object first produces a count-rate spectrum with corrections for
all known instrumental effects. It is computed in the RHESSI spectroscopy object
and can also be generated in the GUI. This count-rate spectrum is then input to the spectroscopy package
- either OSPEX or SPEX. This
converts the count-rate spectrum into the spectrum of the incident photons using
various selectable spectral forms such as thermal and power law.
SPEX, or Spectral Analysis Executive, was written by Richard Schwartz in the
early 1990's. OSPEX, or Object Spectral Analysis Executive, written by Kim
Tolbert in 2004 is the next
generation of SPEX. SPEX will continue to
function as is, but will not be updated. SPEX was developed originally to
analyze spectral information from the Hard X-ray Burst Spectrometer on the Solar
Maximum Mission (SMM) and
from the BATSE instrument on CGRO. It was expanded to include RHESSI in
2002. OSPEX is evolving; it will be enhanced over time and expanded
to include more instruments for analysis. Currently OSPEX includes RHESSI
spectrum and image cube input, as well as SMART-1 XSM, SOXS, MESSENGER, and
FERMI GBM.
OSPEX and SPEX provide a uniform interface suitable for
the spectral analysis of data from a number of solar (or other) instruments in
the X-ray and gamma-ray energy ranges. These packages are suitable for any data
stream that can be placed in the form of response vs. interval, where the
response is usually a counting rate (spectrum) and the interval is normally an
accumulation over time.
Together with an algorithm to relate a model input
spectrum to the observed response, generally a response matrix, the data set is
amenable to analysis with this package. The instrument response matrix details
the probability of a photon of any energy producing a pulse in the detector of a
given amplitude. The response functions for the RHESSI detectors have been
developed by David Smith and are available on line for use with SPEX or OSPEX.
