Abstract

On the 23d of April 2009 a gamma-ray burst was detected by Swift, with unremarkable gamma-ray and X-ray properties. Our UKIRT rapid response programme for GRB follow-up was triggered by an automatic (eStar) system, which revealed a relatively bright source in J, H and K bands. Observations with Gemini-North were obtained soon after, revealing no source to very deep limits at wavelengths lower than ~1 micron, indicating a photometric redshift well above 7. We activated our VLT spectroscopy program for high redshift bursts, and acquired spectroscopy with ISAAC and SINFONI . The spectra give a spectroscopic redshift of 8.23, making GRB 090423 by some distance the most distant object known to date. I will show how the gamma-ray and X-ray optical properties gave little indication of such an extreme redshift, which highlights the need to follow-up every burst with Swift and groundbased facilities. I will discuss how we may be able to use the current and future X-ray, optical and radio facilities to use extremely high redshift GRBs to probe the reionisation and chemical enrichment history of the Universe.