c r r ]{}

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Instrument & Grism & Start time & Exposure time & $\delta t^a$ & Coverage & FWHM\

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& & (UT hh:mm:ss) & (s) & (min) & &\

VLT/FORS2 & — & 08:26:25 & 10 & 36.4 & $R$ band &\
VLT/FORS2 & 300V & 08:32:10 & 600 & 47.1 & 3500–9600 & 13.3\
VLT/FORS2 & 600z+OG590 & 08:43:13 & 600 & 58.1& 8000–9000 & 6.4\
VLT/FORS2 & 1400V & 08:54:37 & 600 & 69.5 & 4600–5900 & 2.5\
ULTRASPEC & — & 08:58:18 & $1.09\times1455$ & 81.4 & $V$ band &\
VLT/FORS2 & 1200R+GG435 & 09:05:47 & 600 & 80.7& 6000–7000 & 3.0\
VLT/FORS2 & 300V & 09:17:11 & 600 & 92.1 & 3500–9600 & 13.3\
VLT/FORS2 & — & 09:30:53 & 45 & 101.2 & $R$ band &\

Long ($>2$ s) soft gamma ray bursts (GRBs) are the most powerful explosions known in the Universe. After the discovery of GRB optical [@VanParadijs97] and X-ray [@Costa97] afterglows in 1997, we have learned that they mainly occur in distant galaxies and their connection to core-collapse supernovae is now widely accepted [for a review see @Woosley06]. The diversity amongst individual GRB events, as well as the difficulty 