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GCN Circular 186

Subject
GRB 981220 and GRB 981226, optical observations
Date
1998-12-31T16:27:27Z (25 years ago)
From
Sylvio Klose at TLS Tautenburg <klose@tls-tautenburg.de>
Sylvio Klose, Thueringer Landessternwarte Tautenburg, Germany, reports:


"The error box of GRB 981220 was observed with the Tautenburg Schmidt 
telescope in the night from Dec. 23 to 24. For any OT at the position
of the radio counterpart of GRB 981220 (Galama et al., GCN #168; Frail
et al., GCN #170) the following preliminary data point can be provided: 
Dec. 23.717 UT, Gunn z >~ 17 +/- 1 mag (observations from 16:48 to 17:36 
UT). A more accurate limit will be published, when photometric standards 
are available. Observations have also been performed in the I-band, but 
do not reach the limiting magnitude reported by Vrba et al. (GCN #171). 
Images are posted on the WWW at http://www.tls-tautenburg.de/research/
grb.html.

The error box of GRB 981226 was observed with the Tautenburg Schmidt
telescope only 6.5 hours after the burst, but under very critical observing 
conditions (zenith distance ~75 deg). For the proposed NIR counterpart
of GRB 981226 (Castro-Tirado et al., GCN #173), the object noted by Galama
et al. (GCN #172), as well as for the variable object reported by Wozniak 
et al. (GCN #177) and Bloom et al. (GCN #182), the following data point can 
be provided: Dec. 26.682 UT, I >~ 16 (observations from 16:07 to 16:40 UT). 
This magnitude limit is based on the Hipparcos star 115941 which has I=7.9 
(see http://astro.estec.esa.nl/hipparcos_scripts/
HIPcatalogueSearch.pl?hipId=115941) and which is very close to the
GRB error circle."

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