Probing cosmic chemical evolution with GRBs

The association of long-duration Gamma Ray Bursts with the final stages of the evolution of massive stars has been established with photometry, via late “bumps” in their optical afterglows, and several cases of direct spectroscopic evidence. The link to massive stars offers their bright afterglow emission as a perfect tool for absorption line spectroscopy of their host galaxy environments and any material along their lines of sight. With typical redshifts of z ∼ 2, and a present record of z = 6.3, it is clear that their afterglows offer a very powerful tool to probe cosmic chemical evolution, to the earliest epochs of star formation, to the epoch of reionization by population III stars and accretion onto rapidly growing black holes. Fast afterglow decline does require a rapid response with very sensitive spectrometers on large aperture telescopes, which is a challenge for current astronomical resources - but rewards are correspondingly high.