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BATSE Trigger Criteria Table | |
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The TRIGGER CRITERIA Table contains a history of the GRB trigger criteria. BATSE will generate a burst trigger if the count rate in two or more detectors exceeds a threshold specified in units of standard deviations above background (nominally 5.5). The rates are tested on three time scales: 64 ms, 256 ms and 1024 ms. The energy range is nominally 50 keV to 300 keV. These efficiencies apply only to the nominal thresholds and energy range. A history of the thresholds and energy range settings is provided in the Trigger Criteria Table. The threshold in flux units depends on the background rate and the sky location relative to the detector normals.
The following table gives the efficiency for generating a burst trigger as a function of peak flux on each of the three trigger time scales. An efficiency of 100% indicates that a burst will always generate a BATSE trigger if it is above the horizon and burst triggering is enabled. Corrections for earth blockage and other flux-independent effects can be made using the sky exposure map. The effects of atmospheric scattering are not included in this table. As a result, the efficiencies at low fluxes are underestimated. The thresholds are sensitive to the spectral shape of a burst. The threshold for a hard burst is lower than the threshold for a softer burst. The table assumes a power-law spectrum with an exponent of -1.5. For an exponent of -2.5, the lower thresholds increase by approximately 20%.
The TRIGGER CRITERIA Table is available for download.
The first column gives the date on which the trigger was changed, the second column gives the truncated julian day (TJD) and the time of day in seconds (SOD) for the trigger change, the third column gives the channels used for triggering, the fourth, fifth, and sixth columns gives the trigger threshold above the background count rate in units of standard deviation on the 64 ms, 256 ms, and the 1024 ms timescales, and the final column gives the first trigger occurring under the new criterion. The channel numbers correspond to the following energy bands:
| Channel 1 | : 20 keV to 50 keV |
| Channel 2 | : 50 keV to 100 keV |
| Channel 3 | : 100 keV to 300 keV |
| Channel 4 | : 300 keV and above |
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Date TJD/SOD Channels Thresholds Trig. #
64 256 1024
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19-Apr-91 2+3 5.5 5.25 5.0
28-Apr-91 8367/5632 5.5 5.5 105
10-May-91 8386/75036 7.0 179
04-Jun-91 8411/68201 5.5 268
18-Aug-92 8852/56078 10.0 1852
24-Aug-92 8858/81762 8.0 8.0 1874
26-Aug-92 8860/78199 10.0 1881
14-Sep-92 8879/70852 5.5 5.5 1928
19-Sep-94 9614/57154 3+4 3175
31-Jan-95 9748/55085 1+2 6.0 6.0 6.0 3386
06-Feb-95 9754/69000 10.0 3405
17-Feb-95 9765/62185 3+4 4.5 4.5 4.5 3434
12-Apr-95 9819/56745 1+2 6.0 6.0 6.0 3504
10-May-95 9847/74116 10.0 3570
20-Jul-95 9918/73523 20.0 10.0 3672
21-Jul-95 9919/62439 10. 3679 *
24-Jul-95 9922/54971 1+2+3+4 26.0 6.0 6.0 3704
28-Jul-95 9926/66825 10.0 3713
05-Sep-95 9965/60364 5.5 5.5 5.5 3778
02-Oct-95 9992/77028 1+2 7.0 3843
23-Oct-95 10013/73672 2+3 5.5 3883
11-Dec-95 10062/77542 1 3.5 3942 **
18-Dec-95 10069/64796 4.0 4027
07-Jan-96 10089/62939 1+2+3 5.5 4263
05-Apr-96 10178/85399 2+3 5413
25-Jun-96 10259/53576 3+4 4.5 4.5 4.5 5520
29-Aug-96 10324/77818 2+3 5.5 5.5 5.5 5589
05-Nov-96 10392/70428 1+2 7.0 5657 ***
25-Feb-97 10504/80816 2+3 5.5 6102
19-May-98 10952/52786 3+4 6765
31-May-98 10964/67660 1+2 7.0 6801
25-Aug-98 11050/71130 3+4 5.5 7019
30-Aug-98 11055/54346 1+2 7.0 7034
28-Sep-98 11084/69980 3+4 5.5 7132
27-Jan-99 11205/75731 2+3 7356
16-Sep-99 11437/72219 1+2 7768
20-Sep-99 11441/72476 2+3 7771
04-Feb-00 11578/51480 4 7981
14-Feb-00 11588/73920 3+4 7989
* Trigger requires that only one detector be above threshold. No gamma-ray bursts were detected.
** Trigger uses detector modules 2 and 3 only.
*** Flight software crash on TJD/SOD 10416/16897 which was fixed TJD/SOD 10418/73555.
| Author | BATSE GRB Team |
| Responsible Manager | Steve Elrod |
| Site Curator | Valerie Connaughton |