GCN Circular 8173

S. Korotkiy (Ka-Dar Observatory), T. Kryachko, B. Satovskiy (Astrotel 
Observatory, KSU/AST) and D. Denisenko (IKI) report:

We have observed the error box of Swift gamma-ray burst GRB 080903 
(Grupe et al., GCN 8169
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 ) with 0.3-m f/7.8 Astrotel-Caucasus telescope (+ 
Apogee Alta U9000 CCD camera) at Kazan State University Mountain Station 
(Karachay-Cherkessia, Russia).  The first 120-sec unfiltered exposure 
was taken at 01:18:21 UT, 358 seconds after the burst trigger.  Inside 
the XRT error circle we have found a new source not present on DSS 
plates at the following coordinates (J2000.0):

05 47 10.05 +51 15 50.9

(astrometry relative to USNO-A2.0 catalogue, accuracy +/-0.2").

Using the nearby USNO-A2.0 1350-06155883 (05 47 16.36 +51 15 56.4) with 
R=18.1 as a comparison star, we have measured CR (unfiltered with Red 
zero point) magnitude 19.1 for the afterglow candidate.  The limiting 
magnitude of the image is 20.5.

Four additional images were obtained with the approaching twilight and 
brightening sky background.  The object is still present on the second 
120-sec exposure obtained at 01:22:09 UT, but not detected on the next 
images.

The crop of Astrotel-Caucasus image is available at:

http://www.astroalert.su/files/grb080903_crop_x4_size.jpg

Color-combined (BRIR) DSS image of the same area for comparison:

http://hea.iki.rssi.ru/~denis/GRB080903-BRIR-crop.jpg