Photometric redshift accuracy for GRB 090423 with different photometric errors. From top left to bottom right, the analysis was performed with the g′,   r′,   i′,   z′,   J,   H,   K_s data of Tanvir et al. (2009) but with photometric errors of  ±0.03 mag,  ±0.06 mag,  ±0.15 mag and  ±0.25 mag respectively. The black line corresponds to the 1σ contour, while the increasingly dark shaded areas correspond to the 90%, 95.4% (2σ), 99%, 99.73% (3σ) and 99.99% confidence contours. The vertical dashed line denotes the spectroscopic redshift.