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The long gamma-ray burst (GRB) rate is essential for revealing the connectionbetween GRBs, supernovae and stellar evolution. Additionally, the GRB rate athigh redshift provides a strong probe of star formation history in the earlyuniverse. While hundreds of GRBs are observed by Swift, it remains difficult todetermine the intrinsic GRB rate due to the complex trigger algorithm of Swift.Current studies usually approximate the Swift trigger algorithm by a singledetection threshold. However, unlike the previously flown GRB instruments,Swift has over 500 trigger criteria based on photon count rate and additionalimage threshold for localization. To investigate possible systematic biases andexplore the intrinsic GRB properties, we developed a program that is capable ofsimulating all the rate trigger criteria and mimicking the image triggerthreshold. We use this program to search for the intrinsic GRB rate. Oursimulations show that adopting the complex trigger algorithm of Swift increasesthe detection rate of dim bursts. As a result, we find that either the GRB rateis much higher than previously expected at large redshift, or the luminosityevolution is non-negligible. We will discuss the best results of the GRB ratein our search, and their impact on the star-formation history.

Probing the Gamma-Ray Burst Rate with Trigger Simulations of the Swift Burst Alert Telescope