GCN Circular 9190

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

report:

The optical afterglow of GRB 090418A (Chornock et al., GCN 9148
Not found
 
 
, Mangano et
al., GCN 9149
Not found
 
 
) was observed with Russian-Turkish 1.5-m telescope (RTT150,
Bakirlitepe, TUBITAK National Observatory, Turkey) under moderate
transparences. We obtained series of 600s exposures in BVRc filters,
centered at April 18, 23:40 UT, i.e. 0.52 days after the burst.

The afterglow is clearly seen at combined R image, and marginally detected
at combined B,V frames.

Using the same calibration star USNO-B1.0 1234-0288651 as Pavlenko et
al. (GCN 9179
Not found
 
 
), we estimate the following magnitudes of OT:

Filter, Exposure, mag.,     err.
         (s)
B       3x600     23.5    limit
V       3x600     22.7    limit
R       4x600     22.1    +/- 0.1

We made also series of 3x900 sec exposures in Rc filter centered on April
20, 23:00, i.e. 2.5 days after the burst. The afterglow was not detected on
the combined frame with a limit R=23.3 mag

RTT150 finding chart (Rc) can be found at:

http://hea.iki.rssi.ru/grb/090418a/indexeng.html