[1] West Virginia Univ, Dept Phys & Astron, Morgantown, WV 26506 USA
[2] West Virginia Univ, Ctr Gravitat Waves & Cosmol, Chestnut Ridge Res Bldg, Morgantown, WV 26505 USA
[3] Green Bank Observ, POB 2, Green Bank, WV 24944 USA
[4] Univ Cologne, Phys Inst, Zulpicher Str 77, D-50937 Cologne, Germany
[5] Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn, Germany
[6] Aix Marseille Univ, LAM, CNES, CNRS, Marseille, France
[7] Penn State Univ, Dept Astron & Astrophys, 525 Davey Lab, University Pk, PA 16802 USA
[8] Univ Maryland, Dept Astron, College Pk, MD 20742 USA
[9] Leiden Univ, Leiden Observ, POB 9513, NL-2300 RA Leiden, Netherlands