[vsnet-grb-info 7668] GRB 090423: Refined TNG analysis

[GCN Circulars]

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  <guidorzi at 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), 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.