The measurement of redshifts for Gamma-Ray Bursts ( GRBs ) is an important issue for the study of the high redshift universe and cosmology .
We are constructing a program to estimate the redshifts for GRBs from the original Swift light curves and spectra , aiming to get redshifts for the Swift 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 .
In this paper , we test the accuracy of our method on 107 bursts with known spectroscopic redshift .
The reduced \chi ^ { 2 } of our best redshifts ( z _ { best } ) compared with known spectroscopic redshifts ( z _ { spec } ) is 0.86 , and the average value of log _ { 10 } ( z _ { best } / z _ { spec } ) is 0.01 , with this indicating that our error bars are good and our estimates are not biased .
The RMS scatter of log _ { 10 } ( z _ { best } / z _ { spec } ) is 0.26 , with a comparison of 0.30 for RMS of log _ { 10 } ( z _ { spec } ) .
We made a selection on bursts with relatively accurate redshift estimation .
The RMS of log ( z _ { best } / z _ { spec } ) decreases to 0.19 , and the RMS scatter of log _ { 10 } ( z _ { spec } ) for this subsample is 0.28 .
For Swift bursts measured over a relatively narrow energy band , the uncertainty in determining the peak energy is one of the main restrictions on our accuracy .
Although the accuracy of our z _ { best } values are not as good as that of spectroscopic redshifts , it is very useful for demographic studies , as our sample is nearly complete and the redshifts do not have the severe selection effects associated with optical spectroscopy .