Discovery of an optical flare from GRB 060926 by the MASTER robotic telescope: Possible formation of a marginally rotating black hole

The MASTER robotic telescope has obtained the first optical images of GRB 060926. We have discovered an optical flare from GRB 060926, a recurrent brightening that closely follows its behavior in the X-ray range. We have determined the spectral slope for GRB 060926 from the X-ray to optical range in the first minutes. Based on the spinar model, we show that the parameters of the optical and X-ray flares suggest that the gamma-ray burst resulted from the core collapse of a 7M ⊙ star with an initial effective Kerr parameter of 7.6 and an initial magnetic-to-gravitational energy ratio of 10−4.