1. Astrophysics Research Institute, Liverpool John Moores University , Liverpool Science Park, 146 Brownlow Hill, UK Liverpool L3 5RF, UK
2. Department of Physics and Earth Science, University of Ferrara , via Saragat 1, I-44122 Ferrara, Italy
3. INFN – Sezione di Ferrara , via Saragat 1, I-44122 Ferrara, Italy
4. INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna , Via Piero Gobetti 101, I-40129 Bologna, Italy
5. Department of Physics, University of Bath , Claverton Down, Bath BA2 7AY, UK
6. Center for Astrophysics and Cosmology, University of Nova Gorica , Vipavska 13, 5000 Nova Gorica, Slovenia