An optical spectrum of the afterglow of a γ-ray burst at a redshift of z = 6.295

摘要: The γ-ray burst GRB 050904, detected by the Swift satellite on 4 September last year, is one of most distant objects ever observed. Its redshift z = 6.3 equates to an explosion taking place 12.8 billion years ago, when Universe was a mere 890 million old. Three groups this week present detailed observations γ-ray, X-ray, near-infrared and optical spectra afterglow 050904. results begin paint picture conditions prevailing parent body exploded suggest that bursts we see in future can be used cosmologists probe early for evidence star galaxy formation, nucleosynthesis reionization. prompt emission from (GRBs) should detectable out distances > 10 (ref. 1), therefore provide excellent evolution cosmic reionization intergalactic medium, metal enrichment history Universe1,2,3,4. Hitherto, highest measured has been 4.50 5). Here report spectrum 050904 obtained 3.4 days after burst; shows clear continuum at long-wavelength end with sharp cut-off around 9,000 A due Lyman α absorption ≈ (with damping wing). A system lines heavy elements 6.295 ± 0.002 also detected, yielding precise measurement redshift. Si ii fine-structure dense, metal-enriched environment progenitor GRB.