Gamnla-ray bursts from the early Universe: predictions for present-day and future instruments

Long gamma-ray bursts (GRBs) are important for the study of the Universe near and beyond the epoch of reionization. In this paper, we describe the characteristics of an 'ideal' instrument that can be used to search for GRBs at z >= 6-10. We find that the detection of these objects requires soft-band detectors with high sensitivity and a moderately large field of view. In light of these results, we compare available and planned GRB missions, deriving conservative predictions of the number of high-redshift GRBs detectable by these instruments along with the maximum accessible redshift. We show that the Swift satellite will be able to detect various GRBs at z >= 6, and likely at z >= 10 if the trigger threshold is decreased by a factor of similar to 2. Furthermore, we find that INTEGRAL and GLAST are not the best tools to detect bursts at z >= 6, the former being limited by the small field of view, and the latter by its hard energy band and relatively low sensitivity. Finally, future missions (SVOM, EDGE and, in particular, EXIST) will provide a good sample of GRBs at z >= 6 within a few years of operation.