1. Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
2. Instituto de Astronomía, Universidad Nacional Autonoma de México, Av. Universidad 3000, C.U., Coyoacán, 04510 Ciudad de México, CDMX, México
3. Facultad de Ciencias Naturales y Matemática, Universidad de El Salvador, Final 25 Avenida Norte, 01101 San Salvador, El Salvador
4. Department of Physics, Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
5. School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
6. Black Hole Initiative at Harvard University, 20 Garden Street, Cambridge, MA 02138, USA
7. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
8. Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109, USA
9. Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA
10. Department of Physics and Astronomy, University of Southampton, Southampton, Hampshire SO171BJ, UK
11. Department of Physics, University of Alberta, 4-183 CCIS, Edmonton, AB T6G 2E1, Canada
12. International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
13. Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), Italy
14. Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany
15. Department of Physics, McGill University, 3600 rue University, Montreal, QC H3A 2T8, Canada