Mathematics – Logic
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.1002x&link_type=abstract
American Astronomical Society Meeting 210, #10.02; Bulletin of the American Astronomical Society, Vol. 39, p.106
Mathematics
Logic
Scientific paper
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 about 60% of the Swift bursts without optical redshifts, and to result in a complete Swift redshift catalog. We are deriving the luminosity indicators from the light curves and spectra of each burst, including the lag time between low and high energy light curves, the variability, 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 be related directly with the luminosity, and we are combining their independent luminosities into one weighted average. Also, we adopt the concordance cosmological model corresponding to a flat universe with Omega = 0.27 and w = -1. Then with our combined luminosity value, the observed burst brightness, and the concordance redshift/distance relation, we can derive the redshift for each burst. Thus, we are going from the Swift light curves and spectra to their redshifts, even without optical observations. We have tested the accuracy of this method by applying it to 69 bursts with known spectroscopic redshifts ranging from 0.17 to 6.6. So far the 1-sigma error of our redshifts is 26%. 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. Our current redshift accuracy of 26% can be improved in the near future through various means; for example, incorporating Firmani’s relation and deriving the luminosity indicators from light curves that have constant energy bands in the burst rest-frame.
Schaefer Bradley E.
Xiao Limin
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