1. Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA.
2. Center for Gravitational Waves and Cosmology, West Virginia University, Chestnut Ridge Research Building, Morgantown, WV 26505, USA.
3. Adjunct Astronomer at the Green Bank Observatory, P.O. Box 2, Green Bank, WV 24944, USA.
4. I. Physik. Institut, University of Cologne, Zülpicher Str. 77, 50937 Cologne, Germany.
5. Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.
6. Aix Marseille Université, CNRS, CNES, LAM, Marseille, France.
7. Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802, USA.
8. Department of Astronomy, University of Maryland, College Park, MD 20742, USA.
9. Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, Netherlands.