TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3262
SUBJECT: GRB 050408: RTT150 optical observations 
DATE:    05/04/14 07:29:26 GMT
FROM:    Irek Khamitov at TUG  <irekk@tug.tug.tubitak.gov.tr>

I. Bikmaev, N. Sakhibullin (KSU/AST), Z. Aslan, I. Khamitov (TUG),
U. Kiziloglu (METU), A. Alpar (SabUni), R. Burenin, M. Pavlinsky,
R. Sunyaev (IKI), report:

     We have observed OT of GRB 050408 (A. de Ugarte Postigo et al., GCN 
3192) with Rc-filter and ANDOR CCD at the Russian-Turkish 1.5-m telescope
(RTT150, Bakyrlytepe, Turkey). We have made a set of 30 exposures with
5 min duration  each during UT 18:30 - 20:10 , April 13. The weather was 
clear with average seeing of 1.8 arcsec.

     We have marginaly detected the OT at the limit of co-added frame with
Rc = 23.7 +/-0.2 mag.

     We have re-reduced our previous observations (Aslan et al, GCN 3198)
by using Landolt standard stars.

RTT150 photometry of OT is given below:

  t-t0 (hours)        Rc    err         exposure
  midtime                               (sec)
   3.72             21.01   0.07        900  (30*30s)
   4.37             21.10   0.05        1080 (18*60s)
   4.89             21.25   0.05        960  (16*60s)
   5.39             21.27   0.05        960  (16*60s)
   5.79             21.44   0.06        960  (16*60s)
   6.55             21.37   0.06        720  (12*60s)
   6.85             21.50   0.06        720  (12*60s)
   8.24             21.64   0.07        1200 (20*60s)
   8.75             21.60   0.07        1200 (20*60s)

123.78             23.7    0.2         9000 (30*300s)

    The power law decay index  between 3.7h and 8.7h calculated on the 
basis of the RTT150  data in Rc-band is -0.68+/-0.06 and the newly 
obtained value of Rc = 23.7 shows that the lightcurve is still fit by a 
single power law of -0.7 (GCN 3215, GCN 3222, GCN 3254).

RTT150 optical light curve of OT GRB050408 is shown at
http://www.tug.tubitak.gov.tr/~irekk/grb/grb050408/lc.jpg

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