A BRIEF EXPLANATION OF ULYSSES GRB DATA
The time histories of solar or cosmic bursts are recorded in either real-time or triggered mode, or both, depending on their intensity. (Refer to the article in Astron. Astrophys.Supp. 92(2), 401, 1992 for more details about the Ulysses GRB experiment). In the real time mode, the time resolution is 0.25, 0.5, 1, or 2 s, depending on the telemetry rate available. There is usually only one energy channel, covering from ~25 - 150 keV. The counts are compressed on the spacecraft, and are then decompressed in the course of data processing on the ground. The counts are compressed according to thefollowing algorithm:
Counts recorded on spacecraft = INT (2*Actual counts)0.5
The counts are decompressed according to this algorithm:
Decompressed Counts = 0.5 * (Counts recorded on spacecraft2 + Counts recorded on spacecraft)
In the triggered mode, the time resolution is either 8/1024 or 32/1024s, depending on the operating mode of the experiment, which can be changed by command (usually, it is 32/1024 s). The counts in the triggered mode are not compressed. The energy channel is again ~25-150 keV, but 16 channel energy spectra are also recorded with a variable, lengthening time resolution, which starts at 1 second. While the experiment is recording triggered data, it continues to record real-time data.
The NSSDC and ESTEC archives contain only the real time data, since the experiment switches automatically and unpredictably between the real-time and triggered modes, and their desire was to have a relatively simple data archive. (Although simple, it is not short: the GRB experiment has been operating almost continuously for over 10 years now, and all the real-time data are in the archives!) We have waived our proprietary data rights period, and routinely send data to the archive as soon as it is available in its final, CD-ROM form (usually about two months after receipt on the ground). Although we are neither required nor funded to do so, we can make small sets of triggered data available to investigators as time and money permit, for specific studies. Contact
Link to ESTEC archive (allows data retrieval, as well as plotting of the data - see example below)
A ~one-year record of the GRB count rate, plotted using the ESTEC
interactive archive.
Link to NSSDC archive (allows data retrieval)