# # Trigger Criteria Table # # The BATSE instrument can trigger on various energy ranges and photon count # rate thresholds. This provides an opportunity to selectively monitor for # transient events with characteristic spectral properties. For instance, the # instrument is most sensitive to gamma-ray bursts when the trigger energy # covers 50 keV to 300 keV, and it is most sensitive to terrestrial gamma-ray # flashes when the trigger energy is 100 keV and above. Changes in count # threshold can affect the triggering on event of a particular duration or # characteristic peak flux. For instance, a high threshold on the 1024 ms # timescale and a low threshold on the 64 ms timescale when triggering on the # energy range 20 keV to 100 keV makes the instrument more sensitive to soft # gamma-ray repeaters and less sensitive to solar flares. # # The table below gives the starting date and time for each trigger criterion # used by the BATSE instrument. 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 is # 20 keV to 50 keV, channel 2 is 50 keV to 100 keV, channel 3 is 100 keV to # 300 keV, and channel 4 is 300 keV and above. This table was last updated on # May 1, 1997. # # BATSE Trigger Criteria History # # ------------------------------------------------------------------- # Date TJD/SOD Channels Thresholds Trig. # # 64 256 1024 # ------------------------------------------------------------------- 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 # * 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. # ----------------------------------------------------------------------------