National Aeronautics and Space Administration

The SAS-2 Archive

Experiment	Images	Raw
Spark Chamber	FITS, GIF	FITS

The SAS-2 data can be obtained using the databases SAS2MAPS, for the high level products, SAS2RAW , for the raw data, or directly from the SAS2 FTP area in the HEASARC archive. The SAS-2 databases can be accessed via Browse.

High Level Products : The SAS-2 data products consist of maps obtained from the 28 SAS-2 observations made during the entire mission. There are 3 sets of maps per observation, extracted over different energy ranges. The energy ranges are as follows: "low" (35-100 MeV), "high" (100-1000 MeV), and "total" (35-1000 MeV). Each set includes three maps: a "counts" map, an "exposure" map, and a "flux" map. The "flux" map was obtained by dividing the "counts" map for the "exposure" maps. Each observation, therfore, has 9 associated maps. These maps are provided in FITS and GIF format.

The SAS-2 data products were created using the program FADMAP (see Software). Each of the FITS maps are 61 X 61 pixels with 1 degree per pixel. Header keywords record the parameter values used in fadmap (see below) to create the maps. The FITS images may be displayed using any standard package which accepts FITS images.

Raw data: The final archive of the 13056 photons detected by SAS-2 consists of 28 FITS files, one for each observation interval. The original data came from 2 sources. The photon information was obtained from the Event Encyclopedia, and the exposures were derived from the original "Orbit Attitude Live Time" (OALT) tapes stored at NASA/GSFC. These two data sets were combined into FITS format by HEASARC using an event layout with three extensions: good time interval (EXTNAME = 'ALLGTI'), event (EXTNAME = 'EVENTS'), and housekeeping (EXTNAME = 'TSI'). The FITS files were created by combining three SAS-2 data sets: a pointing file (OBSDAT), an exposure file (OALT.DAT) and a photon file (ASUMDB.DAT). The photons were stored in the ASUMDB.DAT file. Photon positions (RA and DEC) were converted to pixels within a 512 X 512 pixel pseudo-image array.

The program fadmap can be used on the raw data files to generate maps with different parameter setups or different time selections from those used for the high level products.