Quantifying the Luminosity Evolution in Gamma‐Ray Bursts

We estimate the luminosity evolution and formation rate for over 900 GRBs byusing redshift and luminosity data calculated by Band, Norris, $&$ Bonnell(2004) via the lag-luminosity correlation. By applying maximum likelihoodtechniques, we are able to infer the true distribution of the parent GRBpopulation's luminosity function and density distributions in a way thataccounts for detector selection effects. We find that after accounting for datatruncation, there still exists a significant correlation between the averageluminosity and redshift, indicating that distant GRBs are on average moreluminous than nearby counterparts. This is consistent with previous studiesshowing strong source evolution and also recent observations of under luminousnearby GRBs. We find no evidence for beaming angle evolution in the currentsample of GRBs with known redshift, suggesting that this increase in luminositycan not be due to an evolution of the collimation of gamma-ray emission. Theresulting luminosity function is well fit with a single power law of index$L'^{-1.5}$, which is intermediate between the values predicted by thepower-law and Gaussian structured jet models. We also find that the GRBcomoving rate density rises steeply with a broad peak between $1 3$. This rate density qualitatively matches thecurrent estimates of the cosmic star formation rate, favoring a short livedmassive star progenitor model, or a binary model with a short delay between theformation of the compact object and the eventual merger