TITLE:   GCN CIRCULAR
NUMBER:  6983
SUBJECT: GRB071021: Optical+NIR observations
DATE:    07/10/23 19:55:21 GMT
FROM:    Paul Price at IfA,UH  <price@ifa.hawaii.edu>

P.A. Price (IfA, Hawaii), T. Minezaki (IoA, Tokyo), L. Cowie (IfA,
Hawaii), Y. Yoshii (IoA, Tokyo) and Y. Kakazu (IfA, Hawaii) report:

We observed the candidate optical afterglow of GRB071021 (GCN##6968,
6971,6972) with the robotic MAGNUM telescope + MIPS dual-beam imager. 
Some observations were significantly affected by cloud, but images in I,
H and K were obtained through thin clouds.  We do not detect any source
in our images at the candidate afterglow position, to the following 3
sigma limits, derived from the USNO-1B and 2MASS catalogues:

Filter  midtime(UTC)       Exp. time    upper limits
  I     2007-10-22 6.9h    67min         >22.5mag
  H     2007-10-22 7.7h    30min         >20.4mag
  K     2007-10-22 6.1h    33min         >19.8mag

Our K-band upper limit is consistent with the detection of the afterglow
in K band reported by Kawai et al. (GCN 6976; K~21 mag at 2007-10-22
05:38 UTC).

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