[1] CSIC, IEEC, Inst Space Sci, Carrer Can Magrans S-N, Barcelona 08193, Spain
[2] Univ Amsterdam, Anton Pannekoek Inst Astron, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands
[3] Univ Amsterdam, GRAPPA, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands
[4] AF Ioffe Phys Tech Inst, St Petersburg 194021, Russia
[5] Max Planck Inst Kernphys, POB 103980, D-69029 Heidelberg, Germany
[6] Osserv Astrofis Arcetri, INAF, Largo E Fermi 5, I-50125 Florence, Italy
[7] Ist Nazl Fis Nucl, Sez Firenze, Via G Sansone 1, I-50019 Sesto F No Firenze, Italy
[8] Univ Florence, Dipartimento Fis & Astron, Via G Sansone 1, I-50019 Florence, Italy