1. Astronomical Observatory of the Jagiellonian University, Orla 171, PL-30-244 Cracow, Poland
2. Faculty of Physics, University of Warsaw, Pasteura 5, PL-02-093 Warsaw, Poland
3. Centre of New Technologies, University of Warsaw, Banacha 2c, PL-02-097 Warsaw, Poland
4. National Centre for Nuclear Research, Hoża 69, PL-00-681 Warsaw, Poland