Multiple diffraction lines in the synchrotron x-ray topographs of elastically bent silicon single crystals

X-ray topographs of elastically bent silicon crystals taken with continuous spectrum of a parallel synchrotron radiation beam show straight and curved intersecting lines. These lines are interpreted as due to simultaneous reflection by at least two lattice planes. The interpretation is supported by detailed calculations carried out for a double diffraction case ($4\overline{4}2,3\overline{3}1;1\overline{1}1$), in which one reflection ($4\overline{4}2$) is forbidden in single diffraction.