[vsnet-grb-info 6174] GRB080603B: RTT150 optical observations, break in light curves

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7803
SUBJECT: GRB080603B: RTT150 optical observations, break in light curves
DATE:    08/06/04 09:46:50 GMT
FROM:    Irek Khamitov at TUG  <irekk at tug.tug.tubitak.gov.tr>

R. Zhuchkov, I.Bikmaev, 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 counterpart (GCN7792, 7793, 7794, 7795, 7796, 7797, 7799)
of GRB 080603B (GCN 7794, SWIFT trigger=313087) was observed with
Russian-Turkish 1.5-m  telescope (RTT150, Bakirlitepe, TUBITAK
National Observatory, Turkey), starting at  03 June, 20:55 UT,
i.e. ~1.3 hours after the burst, using Andor CCD.

A series of 70 frames with 60sec exposure in the R and V bands were taken 
for a time span ~ 4.5 hours. The afterglow is clearly detected  in all 
images. Using RTT150 preliminary calibrated magnitudes for USNO-A2 
1575-03195804 star R.A. = 11 46 09.53,  Dec. = +68 01 51.3,  V=14.2, 
R=13.8 mag, the brightness of the OT was estimated on each frame.

V,R light curves are shown at:

http://www.tug.tubitak.gov.tr/~irekk/grb/grb080603B/GRB080603B_lc.jpg

Higher dispersion at (T-T0) > 4 hours must be due to high airmass
( Z ~ 65-70 degrees).

The VR-light curves are well fitted with two power law decay functions
with a break about 3 hours after the burst.

A power law decay indices were estimated in OT VR-light curves as follow:

before the break
alpha_R=-0.59+/-0.03
alpha_V=-0.60+/-0.03

after the break
alpha_R=-1.14+/-0.09
alpha_V=-1.03+/-0.07

The alpha indices before the break are in good agreement with Klotz et al. 
(GCN7799) calculated for the time span between 1 and 4 hours after
the burst.

-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.