Gas and dust properties in the afterglow spectra of GRB 050730
  We present early WHT ISIS optical spectroscopy of the afterglow of gamma-ray burst GRB 050730. 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 HI absorption causing the DLA is most likely located further out. 
R.L.C. Starling (1), P.M. Vreeswijk (2), S.L. Ellison (3), E. Rol (4),   K. Wiersema (1), A.J. Levan (4,5), N.R. Tanvir (5),...