Images of the afterglow of GRB 090423 taken (left to right) with the Y, J, H and K filters. The absence of any flux in the Y filter is a strong indication that the GRB is very high redshift (Credit: A. J. Levan & N. R. Tanvir)
Spectroscopy of the afterglow of GRB 090423 taken with the VLT ISAAC instrument illustrating the sharp break due to Lyman-alpha absorption (Credit: N. R. Tanvir \& K. Wiersema).
Light curve of GRB 090423 in the infrared and X-ray (Credit: A. J. Levan).