[vsnet-grb-info 2320] GRB051021a: optical observations

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4159
SUBJECT: GRB051021a: optical observations
DATE:    05/10/24 13:59:34 GMT
FROM:    Vasilij Rumjantsev at CrAO  <rum at crao.crimea.ua>

V.Rumyantsev (CrAO), V.Biryukov (SAI, MSU), and A.Pozanenko (IKI) on behalf
of larger GRB follow up collaboration report:

We observed  the SXC error box of HETE-2 GRB051021a (Yoshida et al.,
GCN4116) with 0.6 m telescope (Crimean laboratory of SAI) equipped with FLI
IMG-1001E camera. The series of 60 sec R-band exposures were taken between
October 21,  21:19:01 and October 22, 00:23:24. We clearly detect the
optical afterglow (Fox et al. GCN4120, Swan et al. GCN4120) on stacked
image. Coordinates of the source are RA=01 56 36.37 Dec=+09 04 03.27 (J2000)
with uncertainty of 0.5 arcsec. Preliminary photometry of the stacked image
is following:

Mid time (UT)   Exposure   R
Oct. 21 22:51    146x60     21.9 +/-0.2

Photometry and astrometry of the source are based on USNO-A2.0.
Stacked image can be found in http://grb.rssi.ru/GRB051021a/.

Taken R-band magnitudes (GCNs 4120,  4123) and upper limit reported  in
GCN4138 (Eastman et al.) our results is compatible within statistical error
with single power-law decay light curve alpha ~ -1.6. Also extrapolating
backward  J-band (Reichart et al., GCN 4144) observations to our epoch (Oct.
21 22:51)  we found R-J ~ 1.0 which do not imply a high redshift source.

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