2005A&A...442L..21S

We present early WHT ISIS optical spectroscopy of the afterglow of gamma-ray burst GRB050730. The spectrum shows a DLA system with the highest measured hydrogen column to date: N(HI)=22.1±0.1 at the third-highest GRB redshift z=3.968. Our analysis of the Swift XRT X-ray observations of the early afterglow show X-ray flares accompanied by decreasing X-ray absorption. From both the optical and the X-ray spectra we constrain the dust and gas properties of the host galaxy. We find the host to be a low metallicity galaxy, with low dust content. Much of the X-ray absorbing gas is situated close to the GRB, whilst the H I absorption causing the DLA is most likely located further out.