Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 11568

The Christmas burst GRB 101225A - optical spectroscopy with GTC
2011-01-14T17:35:27Z (13 years ago)
Antonio Deugarte at IAA-CSIC <>
C. C. Thoene, S. Guizy, A. Castro-Tirado, J. Gorosabel (IAA-CSIC) and A.
de Ugarte Postigo (DARK/NBI) report:

We observed the optical counterpart of GRB 101225A (the Christmas burst,
GCN 11493, Racusin et al.) with OSIRIS at the 10.4m GTC on Dec. 27,
starting at 21:20 UT (51h after the trigger). We obtained 2 exposures of
1800s using grism R300B.  We acknowledge the excellent support from the
GTC staff.

The combined and flux-calibrated spectrum shows a smooth, very blue
continuum without any absorption of emission features, consistent with the
spectral observations from WHT (GCN 11502, Wiersema et al.), MMT (GCN
11507, Chornock et al.) and Keck/LRIS (GCN 11563, Fynbo et al.) at
different times after the trigger. The continuum is well fitted using a
power law with F(nu) = nu^(0.9+/-0.5).

Considering the very flat optical light curve, the apparent color changes
in the optical SED, the shape of the X-ray spectrum (GCN 11501, Campana et
al.) and the lack of a host galaxy (GCN 11564, Tanvir et al.), we think
that this object might not be a GRB but rather a compact object from the
MW or the local group. Further follow-up is encouraged to determine the
nature of this peculiar object.

[GCN OPS NOTE(14jan11): Per author's request, the last sentence in the first
paragraph was added.]
Looking for U.S. government information and services? Visit