A Gamma-Ray Burst Trigger Toolkit

Abstract

(Abbreviated) The detection rate of a GRB detector can be increased by using a count rate trigger with many accumulation times Dt and energy bands DE, but the nominal sensitivity is less important than how much fainter a burst could be at the detection threshold as Dt and DE are changed. Predictions of the detection rate depend on the assumed burst population, which can be wildly in error. I base the fiducial rate on the BATSE observations: 550 bursts per sky above a peak flux of 0.3 ph/cm^2/s averaged over Dt=1.024s and DE=50-300 keV. I find that triggering on any value of Dt decreases the average threshold peak flux on the 1.024s timescale by a factor of 0.6. Extending DE to lower energies includes the large flux of the X-ray background, increasing the background count rate; a low energy DE is advantageous only for very soft bursts. Whether a large fraction of the population of bright bursts is soft is disputed; the new population of X-ray Flashes is soft but relatively faint.