[1] UNIV CALIF BERKELEY,DEPT ASTRON,BERKELEY,CA 94720
[2] UNIV CALIF BERKELEY,DEPT PHYS,BERKELEY,CA 94720
[3] UNIV CALIF BERKELEY,CTR PARTICLE ASTROPHYS,BERKELEY,CA 94720
[4] UNIV CAMBRIDGE,INST ASTRON,CAMBRIDGE CB3 0HA,ENGLAND
[5] UNIV STRASBOURG 1,OBSERV STRASBOURG,F-67000 STRASBOURG,FRANCE
[6] MAX PLANCK INST ASTROPHYS,D-85740 GARCHING,GERMANY
[7] OSSERV ASTROFIS ARCETRI,I-50125 FLORENCE,ITALY