GCN Circular 4541

D. Malesani (SISSA/ISAS), P. D'Avanzo (INAF/OABr), G. Chincarini (Univ. 
Milano-Bicocca), G. Tagliaferri, S. Campana, S. Covino, D. Fugazza 
(INAF/OABr), A. Fernandez-Soto (Univ. Valencia), M. Della Valle 
(INAF/OAA), L.A. Antonelli, F. Fiore, S. Piranomonte, and L. Stella 
(INAF/OAR), report on behalf of the MISTICI collaboration:

We observed the afterglow of GRB 060116 (Campana et al., GCN 4519
Not found
 
 
; 
Barthelmy et al., GCN 4531
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). Observations were carried out with the ESO 
NTT telescope in the J and Ks filters. Observations were taken almost 
simultaneously to our VLT I-band observations (D'Avanzo, Malesani & 
Antonelli, GCN 4532
Not found
 
 
), that is ~17 h after the GRB.

We detect the afterglow (Kocevski, Bloom & McGrath, GCNs 4528
Not found
 
 
, 4540
Not found
 
 
) in 
the J and Ks filters. Calibration was performed against the 2MASS 
survey. Comparing our measurements to the limit derived by the VLT 
images, we measure the following colors after correcting for the 
Galactic absorption (E(B-V) = 0.263):

  J-K = 2.5 +- 0.3;
  I-J > 2.9.

These colors are very red. If the I-band nondetection is interpreted as 
a dropout, the inferred redshift is z ~ 6. The very red J-K color may in 
this case suggest some rest-frame dust absorption, as also hinted by the 
large column density present in the X-ray spectrum (Campana et al., GCN 
4529
Not found
 
 
). Alternatively, an even larger redshift (z~7-8) may suppress part 
of the J-band emission.

With the present dataset, however, dust emission at lower redshift 
cannot be excluded.

Further observations and analysis are in progress.

We acknowledge the excellent support of the ESO staff, in particular 
Michael Sterzik and Cedric Foellmi.

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