[1] Univ Alabama, Dept Phys, Huntsville, AL 35899 USA
[2] Natl Space & Technol Ctr, Huntsville, AL 35805 USA
[3] NASA, George C Marshall Space Flight Ctr, Huntsville, AL 35812 USA
[4] Univ Amsterdam, Astron Inst Anton Pannekoek, NL-1098 SJ Amsterdam, Netherlands
[5] Univ Amsterdam, CHEAF, NL-1098 SJ Amsterdam, Netherlands