[1
]Physics and Astronomy Department Galileo Galilei, University of Padova, Vicolo dell’Osservatorio
3, I–35122 Padova, Italy
[2
]INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I–35122 Padova,
Italy
[3
]INFN – Padova, Via Marzolo 8, I–35131 Padova, Italy
[4
]Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstrasse 25/8,
A–6020, Innsbruck, Austria