normalized optical afterglow spectrum, centred on the Ly$\alpha$ absorption line, at the GRB host galaxy redshift. A neutral hydrogen column density fit to the damped Ly$\alpha$ line is shown with a solid line (log $(N_{\mathrm{H\,{\sc I}}}/$cm$^{-2})=21.90\pm0.10$), while the $1\sigma$ errors are shown with dashed lines.[]{data-label="fig4"}](fig4.eps){width="87mm"}

In the 300V combined spectrum (averaged from the two 300V flux calibrated spectra), we identify a damped Ly$\alpha$ absorber (DLA) in addition to a number of absorption lines at $z=2.641\pm0.001$, associated with the host galaxy of the burst. We also identify an intervening system at $z_{\textrm{int}}=2.509\pm0.001$ from and transitions. A list of the lines detected in the low resolution 300V spectrum and their equivalent widths (EWs) is reported in @Fynbo09. We measured the EWs for both 300V epochs and find no evidence for spectral variability in the absorption. For the DLA fit, we derived log $(N_{\mathrm{H\,{\sc I}}}/$cm$^{-2})=21.90\pm0.10$ (Fig. \[fig4\]). The tentative detection of Ly$\alpha$ emission inside the DLA, as seen from the 1D spectrum [@Jakobsson08a], is most likely noise, since it is not detected in the 2D frame.\
A good metallicity estimator is usually the weak transition $\lambda$2026, but for this line is only covered by the low resolution 300V spectrum, allowing only a crude 