GRB Afterglows as a New Probe of the ISM and IGM at High Redshift

Abstract

We summarize results from a study of the metallicity, relative abundances, gas density, and kinematics of dense media in the host environment of two Swift bursts, GRB050730 at z=3.968 and GRB051111 at z=1.549. Both GRB hosts exhibit strong absorption features from excited Si+ and Fe+ ions, indicating an extreme ISM environment that is similar to what is found around massive stars like luminous blue variables (LBV) and Wolf-Rayet stars. The extreme ISM properties have never been observed in intervening quasar absorption line systems beyond the local universe.

6 pages including 4 figures; to appear in the proceedings of the 16th Annual October Astrophysics Conference in Maryland, "Gamma Ray Bursts in the Swift Era", eds. S. Holt, N. Gehrels and J. Nousek