The HEAO-1 A1

artist concept of HEAO-1

* Data Products

  • A1 Map There is a single map file for the A1 available through the HEASARC FTP site. This FITS file contains a skymap given as intensity vs. scan angle and day number. The scan angle is in 1/10 th degrees and the day number is measured with day 1 being 1977 day 231. The day numbers range from day 1 to day 253. The intensity is stored as a single precision floating point number.

  • A1 Lightcurves These are the original NRL (Naval Research Laboratory) produced ELE files packed into FITS files at the HEASARC in the Spring of 1996. Each file consists of two FITS extensions: the count data and pointing information for use in timing correction analysis, and housekeeping and flag information preserved from the original 18432 byte ELE records.
    Each row in the FITS file contains an array of 8192 data points containing counts integrated every 5 milliseconds. These data are stored in a column named COUNTS. Therefore each row consists of a 40.96 second records, constituting a Major Frame.
    This dataset is incomplete; it only contains the module 7 data. Several of the HEAO-1 A-1 instruments failed during the mission. The modules 1,2 and 6 failed within weeks of launch. The Module 7 data are useful because they can be cross-correlated with the A-2 experiment data. Module 7 was the only A-1 instrument located on the spacecraft on the same side of the A-2 experiment. All other A-1 Modules are on the opposite side of the spacecraft.
    Warning: There seems to have been a consistent error in the times associated with each record. This manifested itself in the following manner: Each record in the original NASA ELE format data file contained a start time. The start time for successive records were nominally 40.96 seconds apart, as long as the major frame number was consecutive to the previous record. Occasionally, the start time in a record would not be 40.96 seconds after the previous record's start time, and often the time was LESS. Subsequent cross-correlation of the data with A2 data suggested that when this occurred, the time should just be of the form:
    TIME = (current_major_frame_number - last_major_frame_number) * 40.96
    It is unknown why these time inconsistencies occur, but the remainder of the data in a record has been shown to be consistent in time and coordinates with both the parallel A2 observations and observation logs for the A1 instrument.
    The extracted lightcurves are 137 and they are all avaialble in the HEAO-1 A1 FTP area, however consistency with the A2 data were found only for 63 files. For the others, their integrity cannot be guaranteed. The A1POINT database, available in W3browe and browse, includes only the subset of the 63 lightcurves.

    * Raw data An ADP proposal (PI Paul Hertz) was funded to restore the A1 data. However the output of this effort was not delivered to the HEASARC and we are not aware whether the effort is ongoing.

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    Page authors: Lorella Angelini Jesse Allen
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    Last modified: Tuesday, 21-Apr-2020 13:59:22 EDT