SAS2RAW - SAS-2 Photon Events Catalog
Fichtel, C.E., Hartman, R.C., Kniffen, D.A., Thompson, D.J., Bignami, G.F., Ogelman, H., Ozel, M.E., & Tumer, T. 1975. ApJ, 198, 163. Thompson, D.J. 1993. private communication.
The low fluxes involved in the study of gamma-ray sources make it desirable to minimize the background flux from cosmic-rays. Therefore a low Earth equatorial orbit was chosen having a 2 degree inclination; an apogee and perigee of 610 km and 440 km, respectively; and an orbital period of about 95 minutes. During the short lifetime of the mission, there was some noticable decrease in sensitivity due to deterioration of the spark-chamber gas. The calibration of the SAS-2 experiment was done using both the flight unit and an identical flight spare unit. The range of energy studied at the National Bureau of Standards (NBS) Synchrotron, Gaithersburg, Maryland, was approximately 20 to 114 MeV. The energy range between 200 to 1000 MeV was studied at the Deutsches Elektronen-Synchrotron (DESY), Hamburg, West Germany.
This data can be accessed and analyzed in two ways. The events can be plotted for quicklook observing using the BROWSE on-line command XIMAGE, or a file can be extracted from the database and the analysis FTOOL FADMAP can be used on the file to produce source and background maps from the extracted file.
To run FADMAP, type xp # (where # is a number between 1 and 28, for the desired observation). When the file has been downloaded into your captive account area, run the FTOOL FADMAP, entering the desired FITS file name to be analysed at the prompt. If you have a FADMAP.PAR file already in your account area, you can change the hidden parameters to values other than the default by either editing that file, or by typing any parameters you want to change on the initial command line (type 'fhelp fadmap' from the command line for more details). Fadmap will create 4 files: 'source count', 'source exposure', 'modified background count' and 'modified background exposure'. These files can be further analyzed by running the FTOOL FARITH from your captive account. One option is to first divide the 'source count' map by the 'source exposure', divide the 'background count' map by the 'background exposure' map, then subtract the first resultant file by the second. This will give a fairly accurate 'intensity' map. For more information SAS-2 data analysis, consult the on-line "Explanatory Supplement to the SAS-2 database". See the references section of this dbhelp entry for more information
The Right Ascension (1950) in degrees of the optimum observation direction. With a FOV of approximately 35 degrees, photons associated with a particular observation should be within 35 degrees of this RA.
The Declination (1950) in degrees of the optimum observation direction. With a FOV of approximately 35 degrees, photons associated with a particular observation should be within 35 degrees of this DEC.
Original SAS-2 observation identification number. Numbered from 01 to 28.
The start time of the observation. The time is displayed in the format 'yy.ddd' where yy is the last two digits of the year and ddd is the day number within the year (cf: 73.118, is 1973, day 118)
The stop time of the observation. The time is displayed in the format 'yy.ddd' where yy is the last two digits of the year and ddd is the day number within the year (cf: 73.118, is 1973, day 118)
The source name. If one does not exists, this parameter defaults to 'N/A'.
Elapsed time between start of an observation file and the end of an observation file. Inclusive time, in seconds of entire observation.
The sum of all the continuous, uninterrupted exposures within an observation in seconds. Exposure is approximately the "up-time" of the instrument during each of the 28 observations.
The number of photons collected during an observation. Dividing PHOTONS by EXPOSURE gives an approximate value for the flux of an observation.
The BROWSE object classification flag.
The name of the events file in the archive associated with each observation. File is of the form s2_hhmmVddP**t_b.xxx, where s2 is the instrument (SAS-2), hhmm is the right ascension in degrees and minutes, V is N for positive declinations and S is for negative declination, dd is the declination in degrees, P is for 'Pointed' observations '**' is the original observation number, from 01 to 28, t is the datafile 'type' (b for 'background', s for 'source'), b is the 'band' (l for 'low', h for 'high', and f for 'full') and xxx is the FITS file 'type' (img for 'image', exp for 'exposure', flux for 'modified flux map' or gif for 'graphical image format').