The EXOSAT Raw data


artist concept of EXOSAT in space

* Raw data native format : The FOTs

The EXOSAT raw data were distributed to observers as Final Observation Tape (FOT) in form of 1600 BPI tape. Starting from 1992 a total of ~ 8643 tapes (1600 BPI) have been archived in ESRIN/ESA onto optical disk by the ESIS project, and an exact copy has been given to HEASARC/GSFC (Greenbelt, MD, USA). The data volume for the entire mission (all instruments) is 150 Gbyte. At the HEASARC the FOT files have been placed on line in the EXOSAT raw data FTP area on the legacy.gsfc.nasa.gov machine. The data were made available from the HEASARC on-line system in May 1994. An additional shipment of data arrived in September 1994, and was put on-line in December 1994. Not all the data could be recover because some of the earliest 1600 BPI tapes were badly damaged. There are 53 observations for which data from one (or more) experiment are not available neither in the archive (see list of missing data).
The FOT data are in their binary native format. HEASARC is reformatting the EXOSAT raw data to FITS format.

Software for the Raw Data native format:
To analyse the EXOSAT FOT data is recommended to use the EXOSAT Interactive Analysis (IA) System, This can be obtained from the FTP area at ESTEC/SSD on the astro.estec.esa.nl machine or from the FTP area at HEASARC on the legacy.gsfc.nasa.gov. An overview of the EXOSAT Interactive Analysis Software appeared in Legacy 6 and p. 26 .

* Raw data FITS format

The reformatting of the FOTs in FITS started with the Low Energy Experiments. The FITS files are available on line in the HEASARC FTP area

    LE data For each LE (LE1 and LE2) obervation in the EXOLOG database, the corresponding FOT was translated in FITS file. There are 2221 entries in the EXOLOG marked as LE1 or LE2 observations, but more than one observation can be included in the same FOT. These duplicate observations are 218. In addition for 19 out 2221 the FOT is missing. The total number of FOTs processed is 1984 (see list ) for an total amount of 12.4 Gyg of data (compress size). Each FOT in FITS format consists in a variable number of FITS files. The basic files are a catalog, housekeeping, orbit and event files. The catalog file gives an overview of the observation in particular records time periods where valid data were collected. To each time period of valid data is associated an housekeeping and event file. On the total number of FOTs processed 85 show errors due to corrupted records in the FOT (see list ).

Archive organization of the FITS data The archive of the FITS raw data has been organized in the FTP area in directories one for each observation which will contain data from all the instruments operating during that observation. The directory name is derived from the proposal code and the sequence number as given in the EXOLOG database. The proposal code has been grouped in 9 categories and associated to a 6 digit number, as in the table.
100000      PV            Performance  Verification                          
200000      CAL+TOO+OPS   Calibration+Target of Opportunity+Operational Activities      
300000      LLX           CV+Star                 
400000      HLX           X-ray Binaries          
500000      SNR           SNR                     
600000      EXG           Normal Galaxy           
700000      AGN           AGN                     
800000      CLU           Cluster of Galaxies      
900000      MIS+DEE       miscellaneous and deep fields
The sequence number is added to proposal code number to make the directory name.
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Last modified: Wednesday, 08-Oct-2003 18:36:29 EDT