# Exposure vs Peak Flux Table # # 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%. # # 64 ms 256 ms 1024 ms # Threshold Efficiency Threshold Efficiency Threshold Efficiency # (ph/cm^2-sec) (%) (ph/cm^2-sec) (%) (ph/cm^2-sec) (%) 0.798 0.525 0.399 0.374 0.200 0.345 0.825 1.126 0.412 0.962 0.206 0.874 0.854 2.659 0.427 2.515 0.214 2.282 0.886 7.692 0.443 7.510 0.221 6.864 0.921 14.102 0.461 13.807 0.230 12.464 0.960 22.307 0.480 21.900 0.240 19.757 1.003 30.268 0.502 29.879 0.251 26.950 1.051 39.003 0.526 38.654 0.263 35.085 1.106 48.173 0.553 47.720 0.276 43.495 1.168 57.535 0.584 57.144 0.292 52.898 1.240 67.035 0.620 66.693 0.310 62.781 1.324 76.202 0.662 76.024 0.331 72.333 1.424 84.271 0.712 84.092 0.356 80.937 1.546 88.856 0.773 88.775 0.386 86.426 1.696 92.777 0.848 92.696 0.424 91.100 1.890 96.059 0.945 96.012 0.473 95.123 2.152 98.886 1.076 98.857 0.538 98.281 2.527 99.951 1.263 99.944 0.632 99.696 3.124 99.996 1.562 99.996 0.781 99.988 6.247 100.000 3.124 100.000 1.562 100.000