GCN Circular 4454
Subject
GRB 060108: a dark burst?
Date
2006-01-09T12:48:19Z (18 years ago)
From
Daniele Malesani at SISSA-ISAS,Trieste,Italy <malesani@sissa.it>
D. Malesani (SISSA), P. D'Avanzo (INAF/OABr), S. Piranomonte (INAF/OAR),
G. Chincarini (Univ. Milano-Bicocca), L. Stella (INAF/OAR), and G.
Tagliaferri (INAF/OABr), report:
Following the revised XRT position (Page et al., GCN 4453), we looked
again at our VLT images (D'Avanzo et al., GCN 4452) of GRB 060108 (Oates
et al., GCN 4443; Sakamoto et al., GCN 4445). We still do not detect any
source inside the revised XRT error circle , down to the limit J > 22.3.
Using the flux and the decay law given by Page et al. (GCN 4452), we
measure an optical-to-X-ray spectral index alpha_OX < 0.4 (computed
between 1 keV and 1250 nm, at 0.7 d after the burst). Therefore, GRB
060108 violates the synchrotron limit and can be classified as a truly
dark GRB, according to the definition proposed by Jakobsson et al.
(2004, ApJ, 617, L21).
The lack of absorption in the X-ray spectrum may hint at a high-redshift
event, rather to a very absorbed one.
Further observations in the near infrared are encouraged.
This message can be cited.
[GCN OPS NOTE (09jan06): Per author's request, the "050108" was changed to "060108"
in all 3 places.]