The Astrophysical Journal
The American Astronomical Society
In this work, we explore the effects of burst rate denisty evolution on the observed brightness distribution of cosmological gamma-ray bursts. Although the brightness distribution of gamma-ray bursts observed by the BATSE experiment has been shown to be consisitent with a nonevoloving soruce population observed to redshifts of order unity, evolution of some form is likely to be present in the gamma-ray bursts. Additionally nonevolving models place significant constraints on the range of observed burst luminosities, which are relaxed if evolution of the burst population is present. In this paper, three analytic forms of density evolution are examined. In general, forms of evolution with densities that increase montonically with redshift require that the BATSE data correspond to burst at larger redshifts, or to incorporate a wider range of burst luminosities, or both. Independent estimates of the maximum observed redshift in the BATSE data and/or the range of luminosity from which are large fraction of the observed burts are drawn therefore allow for constraints to be placed on the amount of evolution that may be present in the burst population. Specifically, if recent measurements obtained from analysis of the BATSES duration distribution of the actiona limiting redshift in the BATSE data at Zlim = 2 are correst, the BATSE N(P) distribution is a A=0 universe is inconsistent at a level of ~3 σ with the nonevolving gamma-ray bursts and some for of evolution in the population is required. The sense of this required source evolution is to provide a higher desnisty, larger luminosities, or both with increasing redshift.
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