TITLE:   GCN CIRCULAR
NUMBER:  3864
SUBJECT: GRB050820A: RTT150 optical observations
DATE:    05/08/24 12:26:30 GMT
FROM:    Irek Khamitov at TUG  <irekk@tug.tug.tubitak.gov.tr>

I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.),
I. Bikmaev, A. Galeev, N. Sakhibullin (KSU/AST),
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),

report:

      We have continued  observing the OT of GRB 050820A (GCN 3829) with
the Russian-Turkish 1.5-m telescope (Bakirlitepe, TUBITAK National 
Observatory, Turkey)  on the nights of August 22 and 23  in B,Rc,Ic bands.
      We made a series of exposures between UT 20:23 - 01:33, August 22/23,
and between UT 20:09-00:34, August 23/24, 2005. The afterglow is still 
clearly detected in all bands. Using  Henden's stars (GCN 3845) present
in the frames, we estimated the magnitudes as follow:

   t-t0 	Band mag     merr  exptime
(hours)                   (sec,total)
64.39   B   22.24 -/+ 0.06 7860
64.43   Rc  21.02 -/+ 0.03 3900
64.53   Ic  20.46 -/+ 0.05 3900

87.57   B   22.57 +/- 0.08 5400
87.72   Rc  21.30 +/- 0.04 2700
87.82   Ic  20.87 +/- 0.09 2700

      We note that, on re-examining the co-added image for 21 Aug in B-band
(GCN 3853), we noticed that it included a cosmic ray event close to OT.
More careful  calculation has resulted in a fainter value of B magnitude: 
21.47 +/- 0.06 (40.93h after the trigger).

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