TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5224
SUBJECT: GRB 060605: RTT150 optical observations
DATE:    06/06/06 05:45:23 GMT
FROM:    Irek Khamitov at TUG  <irekk@tug.tug.tubitak.gov.tr>

I. Khamitov (TUG), A.T.Saygac (Ist.Uni), Z. Aslan (TUG), U. Kiziloglu 
(METU), E. Gogus (Sabanci Uni.), S.Alis, O.Onal (Ist.Uni)
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI)
I. Bikmaev, N. Sakhibullin (KSU/AST),

report:

We observed the field around the position of the optical counterpart 
(Rykoff et al. GCN 5220, Page et al., GCN5221) of GRB060605 (Swift trigger 
213630) with the Russian-Turkish 1.5-m telescope (RTT150, Bakirlitepe, 
TUBITAK National Observatory, Turkey), starting at June 05, 23:41 UT, i.e. 
~5.42 hours after the burst. A series of frames was taken (20*60s 
exposures in R) with TFOSC. The afterglow is detected clearly in all 
images. Observations were made under strong wind weather.

Using USNO-B1 star (RA=21:28:40.26, DEC=-06:03:44.5,
R2MAG=15.37) we estimate the following Rc magnitudes for the OT:

    t-t0  m_R     err
    5.62  19.767  0.03
    5.83  19.873  0.03
    6.17  19.911  0.03
    6.37  20.010  0.04

The power-law decay index in R is -1.6+-0.3 between 5.62 and 6.37 hours
after the burst. Comparing our decay slope with that derived from
earlier ROTSE data (Schaefer et al., GCN 5222) we conclude that there
was a break in OT light curve between 1 and 5 hours after the burst.

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