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

ABSTRACT Long Gamma Ray Bursts (GRBs) constitute an important tool to study the Universenear and beyond the epoch of reionization. We delineate here the characteristics of an’ideal’ instrument for the search of GRBs at z ≥ 6 − 10. We find that the detectionof these objects requires soft band detectors with a high sensitivity and moderatelylarge FOV. In the light of these results, we compare available and planned GRBmissions, deriving conservative predictions on the number of high-z GRBs detectableby these instruments along with the maximum accessible redshift. We show that theSwift satellite will be able to detect various GRBs at z ≥ 6, and likely at z ≥ 10if the trigger threshold is decreased by a factor of ∼ 2. Furthermore, we find thatINTEGRAL and GLAST are not the best tool to detect bursts at z ≥ 6: the formerbeing limited by the small FOV, and the latter by its hard energy band and relativelylow sensitivity. Finally, future missions (SVOM, EDGE, but in particular EXIST) willprovide a good sample of GRBs at z ≥ 6 in a few years of operation.Key words: gamma–ray: burst – stars: formation – cosmology: observations.