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GCN Circular 4545

GRB 060116: photometric redshift - the farthest GRB?
2006-01-18T20:26:34Z (18 years ago)
Daniele Malesani at SISSA-ISAS,Trieste,Italy <>
A. Grazian (INAF/OAR), A. Fernandez-Soto (Univ. Valencia), V. Testa 
(INAF/OAR), D. Fugazza, P. D'Avanzo (INAF/OABr), L.A. Antonelli (INAF/OAR), D. 
Malesani (SISSA/ISAS), G. Chincarini (Univ. Milano-Bicocca), G. 
Tagliaferri, S. Campana, S. Covino (INAF/OABr), M. Della Valle 
(INAF/OAA), F. Fiore, S. Piranomonte, and L. Stella (INAF/OAR), report 
on behalf of the MISTICI collaboration:

The near-infrared counterpart (Kocevski, Bloom & McGrath, GCNs 4528, 
4540) of GRB 060116 (Campana et al., GCN 4519; Barthelmy et al., GCN 
4531) was observed again with the ESO VLT, adopting the FORS1 and ISAAC 
instruments. Observations were clustered around 2005 Jan 18.1 UT.

The afterglow is clearly detected in the J, H and K filters, and is seen 
to decline achromatically in J and K, comparing our new measurements 
with those secured during the night of Jan 16 (D'Avanzo et al., GCN 
4532; Malesani et al., GCN 4541). The power law decay index is alpha ~ 1.

The object is also detected in the z band, but is not seen in the I and 
R filters.

By fitting the available photometry with a power law suppressed by 
neutral Hydrogen absorption, we measure a photometric redshift z = 6.7 
and z = 6.6 for the first and second night, respectively. Combining 
together the two datasets, we get z = 6.60, the 1-sigma confidence 
interval being 6.45 < z < 6.75. The observed NIR spectral index 
(rest-frame UV) is quite steep, indicating
significant extinction in the rest frame.

GRB 060116 may thus be the farthest observed GRB, and rank among the 
most distant objects detected to date in the Universe.

We would like to acknowledge the painstaking work of the ESO staff to 
perform our service-mode observations. In particular, the ISAAC NIR 
observations were carried out during technical time. We are particularly 
grateful to Gianni Marconi, Jose Cortes, Lorena Faundez, Elena Mason, 
and Dominique Naef.

This message can be cited.

[GCN OPS NOTE(18jan06): Per athor's request, D. Fugazza was added to the author list.]
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