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GCN Circular 9222

Subject
GRB 090423: Refined TNG analysis
Date
2009-04-24T14:16:29Z (15 years ago)
From
Cristiano Guidorzi at Ferrara U,Italy <guidorzi@fe.infn.it>
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<z<8.5, and a temporal decay 
index 0.50.

[GCN OPS NOTE(24apr09): Per author's request, Marinoni was added
to the author list.]
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