Redshifts of the long gamma-ray bursts

Abstract

The low energy spectra of some gamma-ray bursts show excess components beside the power-law dependence. The consequences of such a feature allows us to estimate the gamma photometric redshift of long gamma-ray bursts in the BATSE Catalog. There is a good correlation between the measured optical and the estimated gamma photometric redshifts. The estimated redshift values for long bright gamma-ray bursts are up to z=4, while for long faint bursts the redshifts cannot be determined unambiguously by this method (they should be up to z=20). The redshift distribution of all the gamma-ray bursts with known optical redshifts agrees quite well with the BATSE-based gamma photometric redshift distribution.