GRB 090423 at a redshift of z ≈ 8.1

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Gamma-ray bursts (GRBs) are produced by rare types of massive stellar explosion. Their rapidly fading afterglows are often bright enough at optical wavelengths that they are detectable at cosmological distances. Hitherto, the highest known redshift for a GRB was z = 6.7 (ref. 1), for GRB 080913, and for a galaxy was z = 6.96 (ref. 2). Here we report observations of GRB 090423 and the near-infrared spectroscopic measurement of its redshift, z = . This burst happened when the Universe was only about 4 per cent of its current age3. Its properties are similar to those of GRBs observed at low/intermediate redshifts, suggesting that the mechanisms and progenitors that gave rise to this burst about 600,000,000 years after the Big Bang are not markedly different from those producing GRBs about 10,000,000,000 years later.

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Figure 1: Rest-frame γ-ray and X-ray light curves for bursts at different redshifts.
Figure 2: TNG spectrum of the near-infrared afterglow.


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We acknowledge the TNG staff for useful support during target-of-opportunity observations, in particular A. Fiorenzano, N. Sacchi and A. G. de Gurtubai Escudero. We thank A. Ferrara for discussions. This research was supported by the Agenzia Spaziale Italiana, the Ministero dell’Università e della Ricerca, the Ministero degli Affari Esteri, NASA and the US National Science Foundation.

Author Contributions Direct analysis of the Swift data: S. Campana, G. Chincarini, C.G., R.M., S.D.B., M.D.P., F.E.M., J.N., J.L.R., G. Cusumano, E.E.F., P.G., S.T.H., J.M., C.B.M., C.P., D.M.P.; analysis of the TNG and photometric data: M.D.V., S. Covino, P.D’A., A.F.-S., C.C.T., L.A.A., F.M., V.D’E., F.F., D.F., L.K.H., E. Maiorano, E. Molinari, S.M.; management of optical follow-up: P.D’A., L.A.A., V.D’E., E. Maiorano, S.M., G.A., P.F., G.L.I., N.M., E.P., S.P., G.T., V.T.; interpretation of the GRB properties: R.S., M.D.V., S. Campana, G. Chincarini, S. Covino, P.D’A., A.F.-S., C.G., R.M., C.C.T., L.A., E.P., L.S., K.H.; modelling of the GRB luminosity function: R.S., M.D.V., S. Campana, G. Chincarini, C.G., D.G., G.T. All authors made contributions through their involvement in the programmes from which the data derive, and contributed to the interpretation, content and discussion presented here.

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Correspondence to R. Salvaterra.

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Salvaterra, R., Valle, M., Campana, S. et al. GRB 090423 at a redshift of z ≈ 8.1. Nature 461, 1258–1260 (2009) doi:10.1038/nature08445

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