TITLE: GCN CIRCULAR NUMBER: 9222 SUBJECT: GRB 090423: Refined TNG analysis DATE: 09/04/24 14:16:29 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy A. Fernandez-Soto (IFCA-Santander), F. Mannucci (INAF-OAA), D. Fugazza (INAF-OAB), L.A. Antonelli (INAF-OAR), S. Campana (INAF-OAB), G. Chincarini (Univ. Bicocca), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB/U. Bicocca), V. D'Elia (INAF-OAR), M. Della Valle (INAF-OACa/ESO), A. Fiorenzano (TNG), C. Guidorzi (Univ. Ferrara), E. Maiorano (IASF-Bo), J. Mao (INAF-OAB), R. Margutti (INAF-OAB/Univ. Bicocca), S. Marinoni (TNG), E. Palazzi (IASF-Bo), C. C. Thoene (INAF-OAB) report, on behalf of a larger collaboration (CIBO): We have performed an in-depth analysis of the TNG spectrum of GRB090423 taken on Apr 23 at 22:16 UT with the NICS/Amici combination (Thoene et al, GCN 9216). We have corrected the wavelength calibration, now based both on the observation of sky features and a fit to the instrument sensitivity. We detect in the spectrum flux at wavelengths lambda>1.1 microns, and a flux compatible with zero below that limit. Interpreting this wavelength as the onset of Lyman alpha absorption in the IGM, this leads us to deduce a value of z~8.1. We have also analysed all the available photometry (GCNs 9200, 9201, 9202, 9206, 9209, 9210, 9213, 9214, 9215, 9217, 9218 and 9220) and find that the data are well fit by an afterglow without intrinsic dust obscuration, a photometric redshift 7.6