GCN Circular 5623

A. Stefanescu, F. Schrey, S. Duscha, G. Kanbach, M. Muehlegger, N.
Primak, H. Steinle (MPE Garching) of the OPTIMA-Burst Team report the
following:

We have observed the OT of GRB 060926 under unfavorable weather 
conditions until it became unobservable at ~18:40 UT. To make 
comparision easier with GCN 5618
Not found
 
 
 (U. Kiziloglu et al.), we have 
callibrated our observations against the R2-magnitudes of 4 nearby 
USNO-B1 stars (1030-0324059, 1030-0324042, 1030-0324039, 1030-0324046). 
We estimate the magnitude of the OT as follows:

    t-t_BAT        exp-time
[min] (mid-exp)     [s]         R_mag
-----------------------------------------------
    35.4             600         20.3 +-0.5
    59.7             600         20.6 +-0.5
    72.7             600         20.7 +-0.7
    90.7             2x 1200     21.0 +-0.7
    101.2            1200        21.1 +-0.7


We fitted these values with a powerlaw with a decay index of 0.73 +-0.1.
This is significantly shallower than the powerlaw between the MASTER 
observations (GCN 5619
Not found
 
 
, V. Lipunov et al.) and ours, with a decay index 
of 0.90 +-0.06 - allthough this could be due to incompatibilities in 
zero-point.

We thank J. Papamastorakis of the University of Crete and his team for 
the possibility to use the 1.3m Telescope at Skinakas Observatory for a 
prolonged period of time.