1. Instituto de Física, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves 9500, 91501-970, Porto Alegre, RS, Brazil
2. Instituto de Astronomia, Geofísica e Ciências Atmosféricas, CEP 05508-900, São Paulo, SP, Brazil
3. International Center for Relativistic Astrophysics Network, (ICRANet), Pescara, Italy
4. Instituto de Ciencias Nucleares, Universidad Nacional Autónoma, de México, Circuito Exterior, C.U., A.P. 70-543, 04510 México D.F., Mexico
5. Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-Universität, Ruth-Moufang-Straße 1, 60438 Frankfurt, am Main, Germany