X-ray (square) and optical (circle) light curves of GRB 130912A and the theoretical model curves. The X-ray data are from the UK Swift Science Data Center (Evans et al. 2009) and transformed to 1.732 keV. In order to reduce the influence of the error of the spectral index on the flux calculation, we used the geometric mean of the lower and upper boundaries of the corresponding X-ray energy band 0.3–10 keV. Proper corrections for extinction in the Milky Way Galaxy have been made. The solid and dashed curves are the theoretical optical and X-ray afterglow prediction with a forward shock.