Gamma ray burst redshift catalog and applications

Abstract

The measurement of redshifts for gamma-ray bursts (GRBs) is an important issue for the study of the high redshift universe and cosmology. We developed a program to estimate the redshifts for GRBs from the original light curves and spectra, aiming to get redshifts for bursts without spectroscopic or photometric redshifts. We derive the luminosity indicators from the light curves and spectra of each burst, including the lag time between low and high photon energy light curves, the variability of the light curve, the peak energy of the spectrum, the number of peaks in the light curve, and the minimum rise time of the peaks. These luminosity indicators can each be related directly to the luminosity, and we combine their independent luminosities into one weighted average. Then with our combined luminosity value, the observed burst peak brightness, and the concordance redshift-distance relation, we can derive the redshift for each burst. We test the accuracy of our method on 107 bursts with known spectroscopic redshift, which shows that our error bars are good and our estimates are not biased. This method was then applied to all Swift long GRBs, and a complete Swift long GRB redshift catalog was constructed. Our redshift catalog and catalog of luminosity indicators has many applications in the demographic studies. An investigation of long lag GRBs was made to test the hypothesis that most long lag GRBs are from our local supercluster. An unbiased GRB luminosity function evolution was estimated, and the constraint on the massive star formation rate was made. We also imported the calculation code of luminosity indicators and redshift into the Fermi GBM data analysis software RMFIT, with which the all the luminosity indicators and the redshift can be calculated within half an hour after the raw data are generated from the pipeline.