1. Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA
2. Department of Physics, Astronomy, Geosciences and Engineering Technology, Valdosta State University, Valdosta GA, 31698, USA
3. Space Science and Astrobiology Division, MS 245-3, NASA Ames Research Center, Moffett Field, CA 94035, USA