1. Physics Department, University of Pisa , Largo B. Pontecorvo 3, I-56127 Pisa, Italy
2. European Gravitational Observatory , Via E. Amaldi, I-56021 Cascina, Pisa, Italy
3. INFN – Pisa , Largo B. Pontecorvo 3, I-56127 Pisa, Italy
4. INAF – Osservatorio Astronomico di Roma , Via Frascati 33, I-00078 Monte Porzio Catone, Rome, Italy
5. INAF – Osservatorio Astronomico di Brera , Via Bianchi 46, I-23807 Merate, Lecco, Italy
6. Physics and Astronomy Department Galileo Galilei, University of Padova , Vicolo dell’Osservatorio 3, I-35122 Padova, Italy
7. INFN – Padova , Via Marzolo 8, I-35131 Padova, Italy
8. INAF – Osservatorio Astronomico di Padova , Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
9. Scuola Normale Superiore (SNS) , Piazza dei Cavalieri 7, I-56126 Pisa, Italy