[1] Russian Acad Sci, Lebedev Phys Inst, Leninsky Prospekt 53, Moscow 119991, Russia
[2] Moscow Inst Phys & Technol, Inst Sky Per 9, Dolgoprudnyi 141700, Russia
[3] Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn, Germany
[4] Crimean Astrophys Observ, Nauchny 298409, Crimea, Russia