High redshift gamma-ray bursts as a probe of the early universe and first stars

Abstract

Gamma-ray bursts (GRBs) are the most violent explosions in the universe. Thanks to their extreme brightness, GRBs can be detected up to the edge of the visible universe. As bright beacons in the deep universe, high-redshift GRBs have been considered as an ideal tool to explore the properties of the early universe: including the dark energy and cosmological parameters, star formation rate, first stars, the reionization and metal enrichment history of the universe. So the detection of high-z GRBs has important scientific significance. Compared to current missions, Einstein Probe has a higher sensitivity and a wider field-of-view, operating the soft X-ray band (0.5–4 keV), which would be suitable for the detection of high-z GRBs. With its observational mode and ability, we compute the expected detection rate of high-z GRBs by Einstein Probe by means of a observational tested population synthesis model of Swift GRBs. Our results show that the detection rates are expected to be about 20 events yr^-1 sr^-1 for z > 6 bursts, 6 events yr^-1 sr^-1 for z > 8 bursts, and 1 events yr^-1 sr^-1 for z > 12 bursts, respectively. Over the 3 yr lifetime of the mission, Einstein Probe will able to detect about 65 GRBs at z > 6, including ∼ 20 GRBs at z > 8 and ∼ 3 GRBs at z > 12. In sum, Einstein Probe would significantly improve the detection of high-z GRBs, and these abundant observational information would probably reveal some scientific mysteries of the early universe.