Title:
Are Gamma-Ray Bursts optically brighter at high-z?
ABSTRACT
We constrain the dominant optical selection e ffects biasing the Gamma-Ray Burst
(GRB) redshift distribution using Swift triggered redshifts acquired from the optical
afterglow. Models for the Malmquist, redshift desert, and dust extinction biases
are used to show how the "true" GRB redshift distribution is distorted to its presently
observed biased distribution. The statistically optimal model shows
that GRB host galaxy dust extinction could account for up to 17% of missing redshifts.
The model also requires an increasing mean optical afterglow luminosity with redshift. This could be explained by a decrease
in dust obscuration in GRB hosts at high-z. Alternatively, the optimal model can also
be obtained without optical afterglow brightness evolution, but requires a source rate
evolution four times higher than the star formation rate at z = 10 compared to z = 0.