Spectral parameters of the prompt emission using the time-resolved XRT-BAT-GBM data. a) The evolution of the photon index from fits to BAT-GBM and XRT data. Open circles show the low-energy index below the break energy E₁ of a single broken power law and the filled circles represent the high-energy index above E₁. Points with no plot symbols (error bars only) are the best-fit results using only a simple power law. b) The low-energy break energy, E₁, from fits to the BAT and XRT data. During the flare at 208 s spectral evolution is seen, similar to what was also detected in other afterglows (e.g., Falcone et al. 2007).