2005/11/16 by E. Berger, B. E. Penprase, Bryan E. Penprase +7 · 5 citations
Physics and Astronomy · #Astro and Planetary Science #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/501162
published as Astrophys.J.642:979-988,2006 · 19 pages, 8 figures, 2 tables; submitted to ApJ
arxiv created 2005/11/16 · openalex publication_date 2006/05/10 · arxiv updated 2010/05/12 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/01
We present optical spectroscopy of the afterglow of GRB 050505 obtained with the Keck I 10 m telescope. The spectrum exhibits three absorption systems with the highest, at z = 4.2748, arising in the host galaxy. The host absorption is marked by a DLA with log N (H ) = 22.05 ± 0.10, higher than that of any QSO-DLA detected to date but similar to several other recent measurements from GRB spectra. We further deduce a metallicity of Z ≈ 0.06 Z ☉ , with a depletion pattern that is similar to that of the Galactic warm halo or warm disk. More importantly, we detect strong absorption from Si II* indicating a dense environment, n H ≳ 10 2 cm -3 , in the vicinity of the burst, with a size of ~4 pc. The C IV absorption system spans a velocity range of about 10 3 km s -1 , most likely arising in the progenitor stellar wind. In this context the lack of corresponding Si IV absorption indicates that the progenitor had a mass ≲25 M ☉ and a metallicity ≲0.1 Z ☉ , 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 ≈ 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 and/or sight lines which probe star-forming regions, or if it is a manifestation of different star formation properties in GRB-DLAs.