Gamma-Ray Bursts And High-redshift Star Formation Rates

Gamma-ray bursts (GRBs for short) are a suddenly enhanced gamma-ray ra-diation from arbitrary direction of the universe, which last from a few milliseconds to thousands seconds. It was first discovered by the "Vela" satellite of American in1967, but the result was later released to the public in1973by considering the military purpose. In1991, the launch of the Compton satellite made us know that: GRB spectrum could be well fitted by the Band function, their duration is a bi-modal distribution, and they are isotropically distributed in our galactic coordinate system. Until1997, the discovery of the GRB afterglow by the "BeppoSAX" satel-lite enable us to make an accurate measurement of the GRB redshift, especially, the bumps appear in the optical afterglow of GRBs make us know that GRBs may correlated with the collapse of the massive stars. From then on, GRB is widely used in the research of cosmology. In December2004, NASA launched a satellite which is specially designed to observe GRB, which is called "Swift". Because of the fast reaction of "Swift", we have enough time to locate the GRB direction by the ground-based telescope and measure the redshift. The biggest contribution of the Swift satellite is its supplement of a large amount of GRBs with redshifts, which is the foundation of GRB as the cosmology tool.Based on the Swift redshift-known GRB sample, we try to find the relationship between the GRB peak luminosity and peak energy, and infer their pseudo-redshift in chapter2. In chapter4and5, we try to constrain the high redshift star formation rates from two aspects.Until recently, BAT have detected nearly800GRBs, however, only200with measured redshifts which is still not enough for the determination of luminosity function (LF). In order to find a larger GRB sample, we suggest calculating pseudo-redshifts for Swift GRBs according to the empirical L-Ep relationship. Using the GRB sample with pseudo-redshifts of a relatively large number, we fit the redshift-resolved luminosity distributions of the GRBs with a broken-power-law LF. The fitting results suggest that the LF could evolve with redshift by a redshift-dependent break luminosity. It is also found that the proportional coefficient between the GRB event rate and the star formation rate should correspondingly decrease with increasing redshifts.The research of the high redshift star formation history is always a hot spot in the astrophysical area. In chapter4and chapter5, we will try to solve this problem from two aspect:(1) By employing a simple semi-analytical star formation model where the formation rates of Population (Pop) Ⅰ/Ⅱ and Ⅲ stars can be calculated, we account for the number distribution of gamma-ray bursts (GRBs) with high pseudo-redshifts that derived from chapter2. It is suggested that a considerable number of Pop Ⅲ GRBs could have existed in the present Swift GRBs. By further combining the implication for the star formation history from the optical depth of the CMB photons, it is also suggested that there could only be a very small fraction (～1%) of Pop Ⅲ GRBs triggered the Swift BAT.(2) By phenomenologically describing the high-redshift star formation history, and semi-analytically calculating the fractions of high-redshift Pop Ⅰ/Ⅱ and Pop Ⅲ stars, we investigate the contributions from both high-redshfit Pop Ⅰ/Ⅱ and Pop Ⅲ stars to the observed near-infrared excess in the cosmic infrared background emission. In order to account for the observational level of the near-infrared excess, the power-law index a of the assumed star formation history is constrained to within the range of0(?)α(?)1.