2006/11/09 by S. Campana, D. Lazzati, E. Ripamonti +7 · 1 citation
Physics and Astronomy · #Afterglow #Astronomy and Astrophysical Research #Galaxy #Gamma-ray burst #Gamma-ray bursts and supernovae #Metallicity #Molecular cloud #Redshift #Spectroscopy #Star formation #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/510719
published as Astrophys.J.654:L17-L20,2006 · 4 pages, 2 figures. Accepted for publication on Astrophysical Journal Letters
arxiv created 2006/11/09 · openalex publication_date 2006/12/13 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
GRB 050904 is the gamma-ray burst with the highest measured redshift. We performed time-resolved X-ray spectroscopy of the late GRB and early afterglow emission. We find robust evidence for a decrease with time of the soft X-ray-absorbing column. We model the evolution of the column density due to the flash ionization of the GRB and early afterglow photons. This allows us to constrain the metallicity and geometry of the absorbing cloud. We conclude that the progenitor of GRB 050904 was a massive star embedded in a dense metal-enriched molecular cloud with Z ≳ 0.03 Z ☉ . This is the first local measurement of metallicity in the close environment of a GRB and one of the highest redshift metallicity measurements. We also find that the dust associated with the cloud cannot be similar to that of our Galaxy but must be either sizably depleted or dominated by silicate grains. We discuss the implications of these results for GRB progenitors and high-redshift star formation.