[1] Univ Tennessee, Dept Phys & Astron, Knoxville, TN 37996 USA
[2] Oak Ridge Natl Lab, Div Phys, Oak Ridge, TN 37831 USA
[3] Oak Ridge Natl Lab, Joint Inst Heavy Ion Res, Oak Ridge, TN 37831 USA
[4] Canadian Inst Theoret Astrophys, Toronto, ON M5S 3H8, Canada
[5] Aarhus Univ, Inst Phys & Astron, DK-8000 Aarhus C, Denmark
[6] Inst Estudis Espacials Catalunya, E-08034 Barcelona, Spain
[7] Inst Catalana Rec & Estudis Avancats, E-08010 Barcelona, Spain