We present the discovery of the optical afterglow of GRB 050505 and an optical absorption spectrum obtained with the Keck I 10-m telescope .
The spectrum exhibits three redshifted absorption systems with the highest , at z = 4.2748 , arising in the GRB host galaxy .
The host absorption system is marked by a damped Ly \alpha ( DLA ) feature with a neutral hydrogen column density of { log } N ( { HI } ) = 22.05 \pm 0.10 , higher than that of any QSO-DLA detected to date , but similar to several other recent measurements from GRB spectra .
In addition , we detect absorption lines from both low- and high-ionization species from which we deduce a metallicity , Z \approx 0.06 Z _ { \odot } , with a depletion pattern that is roughly similar to that of the Galactic warm halo , warm disk , or disk+halo .
More importantly , we detect strong absorption from Si ii* indicating a dense environment , n _ { H } \gtrsim 10 ^ { 2 } cm ^ { -3 } , in the vicinity of the burst , with a size of \sim 4 pc .
In addition , the C iv absorption system spans a velocity range of about 10 ^ { 3 } km s ^ { -1 } , which is not detected in any other absorption feature .
We show that the most likely interpretation for this wide velocity range is absorption in the wind from the progenitor star .
In this context , the lack of corresponding Si iv absorption indicates that the progenitor had a mass of \lesssim 25 M _ { \odot } and a metallicity \lesssim 0.1 Z _ { \odot } , and therefore required a binary companion to eject its hydrogen envelope prior to the GRB explosion .
Finally , by extending the GRB-DLA sample to z \approx 4.3 we show that these objects appear to follow a similar metallicity-redshift relation as in QSO-DLAs , but with systematically higher metallicities .
It remains to be seen whether this trend is simply due to the higher neutral hydrogen columns in GRB-DLAs , or if it is a manifestation of different star formation properties in GRB-DLAs .
Thus , GRBs hold the potential to probe all scales relevant to our understanding of the star formation process and its relation to metal production .