INAF, Osservatorio Astrofisico di Catania, via S. Sofia 78, I-95123 Catania, Italy, Dipartimento di Fisica e Astronomia “Ettore Majorana,” Università di Catania, Via S. Sofia 64, 95123, Catania, Italy, and High Energy Physics Department, Institute of Mathematics, Astrophysics, and Particle Physics, Radboud University, Heyendalseweg 135, 6525 AJ Nijmegen, The Netherlands