Source Density Evolution of Gamma‐Ray Bursts

Recent optical afterglow observations of gamma-ray bursts indicate a settingand distance scale that many relate to star-formation regions. In this paper,we use $$ and a set of artificial trigger thresholds to probeseveral potential GRB source density evolutionary scenarios. In particular, wecompare a uniform subset of BATSE 4B data to cosmological scenarios where GRBsevolve as the comoving density, the star formation rate, the QSO rate, and theSN Type Ic rate. Standard candle bursts with power-law spectra and a universewithout vacuum energy were assumed. Our results significantly favor a comovingdensity model, implying that GRB source density evolution is weaker thanexpected in these evolutionary scenarios. GRB density might still followstar-formation rates given proper concurrent GRB luminosity evolution,significant beaming, significant error in standard candle assumptions, or werea significant modification of star formation rate estimates to occur.Comment: 12 pages, 4 figures, accepted by Ap