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.]