[1] Yale Univ, Dept Phys, New Haven, CT 06520 USA
[2] Yale Univ, Yale Ctr Astron & Astrophys, New Haven, CT 06520 USA
[3] Leibniz Inst Astrophys, D-14482 Potsdam, Germany
[4] Natl Radio Astron Observ, Charlottesville, VA USA
[5] CALTECH, Dept Astron, Pasadena, CA 91125 USA
[6] Univ Wyoming, Dept Phys & Astron, Laramie, WY 82071 USA
[7] Lawrence Berkeley Natl Lab, Berkeley, CA 92420 USA
[8] Univ Paris 06, CNRS, Inst Astrophys Paris, UMR7095, F-75014 Paris, France
[9] Univ Florida, Dept Astron, Bryant Space Sci Ctr 211, Gainesville, FL 32611 USA
[10] Penn State Univ, Dept Astron & Astrophys, University Pk, PA 16802 USA
[11] Penn State Univ, Inst Gravitat & Cosmos, University Pk, PA 16802 USA
[12] Univ Chicago, Dept Astron & Astrophys, Chicago, IL 60637 USA