  For gamma-ray bursts (GRBs) with durations greater than two seconds
(so-called long GRBs), the intrinsic prompt gamma-ray emission appears, on
average, to last longer for bursts at lower redshifts. We explore the nature of
this duration-redshift anti-correlation, describing systems and conditions in
which this cosmological evolution could arise. In particular, we explore its
dependence on metallicity of a massive star progenitor, as we can securely
count on the average stellar metallicity to increase with decreasing redshift.
Although higher metallicity/lower redshift stars lose mass and angular momentum
through line-driven winds, in some cases these stars are able to form more
extended accretion disks when they collapse, potentially leading to longer
duration GRBs. We also examine how this duration-redshift trend may show up in
interacting binary models composed of a massive star and compact object
companion, recently suggested to be the progenitors of radio bright GRBs. Under
certain conditions, mass loss and equation of state effects from higher
metallicity, lower redshift massive stars can decrease the binary separation.
This can then lead to spin-up of the massive star and allow for a longer
duration GRB upon the massive star's collapse. Finally, the duration-redshift
trend may also be supported by a relatively larger population of
small-separation binaries born in situ at low redshift.

High Energy Astrophysical Phenomena