National Aeronautics and Space Administration

The COS-B Archive

Experiment	Images	Raw
Spark Chamber	FITS, GIF	FITS

The COS-B data can be obtained using the databases COSBMAPS, for the high level products, COSBRAW , for the raw data, or directly from the COSB FTP area in the HEASARC archive. The COS-B databases can be accessed via Browse .

High level Products : The COS-B data products consist of maps obtained from the 65 COS-B observations made during the entire mission. There are 4 sets of maps per observation, extracted over different energy ranges. The energy ranges are as follows: "low" (70-150 MeV), "medium" (150-300 MeV), "high" (300-5000 MeV), and "full" (50-7800 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, therefore, has 12 associated maps. These maps are provided in FITS and GIF format.

The COS-B data products were created using the program FADMAP (see Software). Each of the FITS maps are 120 x 120 pixels with 0.5 degrees 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 reduction of the COS-B data, released by ESA in 1985, consisted of three basic datasets: `OBSLI`, describing each observation period (typically one month), `OURLI`, describing each uninterrupted observation interval (lasting between 10 minutes and 10 hours), and `GAMLI`, containing records for each accepted gamma-ray photon. These three data sets were combined into FITS format with an event layout at the HEASARC.

Each event file contains three extensions: good time interval (EXTNAME = 'ALLGTI'), event (EXTNAME = 'EVENTS'), and housekeeping (EXTNAME = 'TSI'). The ALLGTI and TSI extensions contain the information stored in the `OURLI` and `OBSLI` datasets. The EVENTS extension contains data from the `GAMLI` dataset. There are, in total, 65 files, one for each `OBSLI` observation. Photon positions (RA and DEC) were converted to pixels within a 512 X 512 pixel pseudo-image array. Each pixel is 0.1 degrees so the image is 51.2 X 51.2 degrees.

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.