Kim Tolbert 23-May-2019

SMM was in operation from February 1980 to December 1989 and observed 260 gamma-ray solar flares (Vestrand et al. ApJS 120:409-467, 1999). Some information about the Gamma Ray Spectrometer (SMM/GRS) is here: https://umbra.nascom.nasa.gov/smm/grs.html.


------  FULL RESOLUTION SOLAR DATA  ------

The FITS files in these year directories were created from the .USE files (https://umbra.nascom.nasa.gov/pub/smm/smmgrs/solar_flare/) by Kim Tolbert in April 2019 using the programs grs2fits.pro and grs_read_use_file.pro. The FITS files contain all of the data from the .USE files (note - the primary data - rates and energy edges - are in extensions 1 and 2, and the full structure returned by the grs_extract IDL routine is in extension 3).

The files are named smm_grs_yyyymmdd_hhmm_hhmm_xxxxxxFD.fits, ...DB.fits, and ...DA.fits, where
yyyymmdd_hhmm_hhmm is the year, month, day, and start and end hours / minutes of the file,
FD means flare data,
DB means day before flare data,
DA means day after flare data, and
xxxxxx is the original USE file name

The solar flare spectra are in the FD files. The DB and DA spectra are provided for background. 476 logarithmically spaced energy channels are provided at 16.328 s resolution.  The time sequence of DB and DA spectra have been aligned with the flare sequence of flare spectra to provide the best background estimates.

The ..._background.sav files in these directories were created from the DB, DA files and contain the averaged (or just DB or DA) background that can be used to analyze the flare.  Note - the set of files (FD, DB, DA, and background save) that apply to a particular flare all have the same USE file name. A list of flare time intervals and the method used to compute the background in the corresponding .sav file is provided in the GRS_flare_background.txt file in this directory.  

In OSPEX (SSW spectral analysis package https://hesperia.gsfc.nasa.gov/ssw/packages/spex/doc/ospex_explanation.htm), to analyze a flare, set the input spectrum file to the FD file, and let OSPEX automatically find and set the background from the corresponding save file.  The user never needs to use the DB AND DA files - they are available for examination, but their usable background data is already saved in the save files.
After setting the input FD file, the o->grs_bk_from_save method (or button on Background widget) can be used to automatically find the save file corresponding to the input FD file, and set the background from the save file into OSPEX.  Not all flares have a background save file, usually because there was not enough overlapping (i.e. from the same orbital location) data in the FD, DB, DA files.  For those flares you may have to use in-orbit background in the FD file.

When analyzing these data in OSPEX, the response matrix is retrieved from $SSW_OSPEX/grs/gerry_grs_drmnew.sav - there is no flare-dependent response file.  The response matrix was calculated by G. Share using a Monte Carlo code based on one used to calculate the Compton Gamma Ray Observatory OSSE response. 


------  LOW ENERGY RESOLUTION BACKGROUND-SUBTRACTED SOLAR DATA  ------

In the same year directories, there is another set of FITS files containing background-subtracted, energy-grouped data provided by G. Share.  There is one file for each flare that contains the background-subtracted spectrum integrated over the entire flare.  The count rates in sequential data channels were summed so that the rates are significant at at least the 95% confidence level. The minimum number of channels summed is two. This allows for the study of weaker flares at coarser spectral resolution. A list of the accumulation time range, livetime, and number of energy bins for each flare is listed in the GRS_bksub_egrouped_times.txt file.

These files can be analyzed in OSPEX. Background time intervals obviously should not be set in OSPEX since background has already been subtracted.  OSPEX reads the detector response matrix for the compressed count bins from the 3rd extension of the FITS file.

These files are named smm_grs_bksub_egrouped_yyyymmdd_hhmm_hhmm.fits where yyyymmdd_hhmm_hhmm is the year, month, day, and start and end hours / minutes of the file.