TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5002 SUBJECT: GRB060418: Further Analysis of MIKE Spectroscopy DATE: 06/04/24 17:27:34 GMT FROM: Jason Prochaska at UCO/Lick Obs J. X. Prochaska (UCO/Lick Observatory), H.-W. Chen (U Chicago), J. S. Bloom (UC Berkeley), E. Falco, and A. K. Dupree (Harvard-Smithsonian CfA) report on behalf of the GRAASP collaboration: "We have further analyzed the echelle spectra of GRB060418 (Falcone et al. GCN 4966), obtained using MIKE on the Magellan Clay telescope (Dupree et al. GCN 4969). We report the detection of ZnII, SiII, SiII*, FeII, FeII*, MgII, MgI, AlIII, CIV and NiII transitions among others at a redshift z=1.4901 +/- 0.0001. The relative populations of the excited FeII levels are similar to GRB051111 (PHB06, astro-ph/0601057); the J=7/2 to J=1/2 states follow a Boltzmann distribution with T=1000-5000K. But, following GRB051111 and GRB050730, we interpret the FeII excitation as the result of indirect UV pumping by the GRB afterglow. The detection of strong MgI absorption places this gas (and presumably the majority of low-ion gas) at a distance r>50pc from the GRB. Finally, we measure [Si/Fe]=+0.5dex indicating a modest dust-to-metals ratio. This message may be cited."