Ulysses GRB Integral 0.5-Second Omnidirectional Counting Rates

The former deposit energy directly in the scintillator if they are energetic enough, while the latter may produce x- radiation locally by bremsstrahlung. Thus although the counting rates are generally stable at about 500 c/s over the long term, there are periods of weeks to a month or so when the rates increase considerably due to particles. Examples may be found in March 1991 (solar protons) and February 1992 (particles in the Jovian magnetosphere).

The time resolution of the data takes on one of four values depending on the telemetry rate and instrument operating mode: 0.25, 0.5, 1, or 2 seconds. Data rate changes produce short spikes in the count rates due to a processing artefact. These can in principle be corrected if the data are scanned and the rate changes are identified; the count rate spikes can then be adjusted to their correct values.

There are also short (one sample long) count rate dropouts, due to an artefact of the onboard software. These may be seen in the sample plots; they cannot be corrected for. Two figures give examples of solar and cosmic events in the data.

The upper panel gives the count rates for day 142, 1993, around 8.24 hours UT. The solar event is evident as a 300 second long increase. Note the count rate dropouts.

The bottom panel includes a 20 second long cosmic gamma-ray burst from day 237, 1993 around 8.79 hours UT.