Proceedings of ICRC 2001: 3601 c  Copernicus Gesellschaft 2001 ICRC 2001 Heliospheric electrons from Jupiter R. G ´ omez-Herrero 1 , M. D. Rodr´ ıguez-Fr´ ıas 1 , L. del Peral 1 , J. Sequeiros 1 , R. M ¨ uller-Mellin 2 , and H. Kunow 2 1 Dpto de F´ ısica, Universidad de Alcal´ a, E-28871 Alcal´ a de Henares, Madrid, Spain. 2 2 Institut f ¨ ur Experimentelle und Angewandte Physik, Universit¨ at Kiel, D-24118, Kiel, Germany. ___________________ Correspondence to: R. Gómez-Herrero (raul.gomez@uah.es) Abstract. The electron spectrum in the energy range 250 keV to 10 MeV measured by EPHIN sensor onboard SOHO observatory during 1996 quiet time periods is presented. The results show that the dominant electron population is of Jovian origin. The spectral indexes obtained range from 1.5 to 1.8 in this work an estimation of the emission intensity of electrons from the Jovian magnetosphere is also obtained. Unexpected recurrence of Jovian electrons at the middle of 1996, during poor Earth- Jupiter magnetic connection has been observed. _______________________________________________ 1 Introduction There are two dominant sources of interplanetary electrons in the inner heliosphere in the energy range 0.2 to 25 MeV: Solar Energetic Particles (SEP) events and the Jovian magnetosphere. SEP events electrons are observed as sudden and intense increases in the intensity of energetic electrons in connection with solar flares and/or CMEs occurrences. During solar quiet time periods, the dominant population in this energy range is of Jovian origin. The First evidence that the Jovian magnetosphere releases a great number of electrons into interplanetary space was obtained in 1973, when Pioneer 10 approached Jupiter (Teegarden et al., 1974). Jovian electron intensity near Earth fluctuate depending on magnetic connection between Earth and Jupiter, with a 13 months periodicity (synodic period of Jupiter). Expected galactic electron flux at 1 AU is a factor of 50 or more below the observed 12 MeV electron flux (Eraker, 1982). Observation of Jovian electrons near Earth is a valuable source of information for the study of propagation of energetic electrons in the inner heliosphere, but it is an obstacle for the study of Galactic Cosmic Ray electrons modulation process. 2 Instrumentation EPHIN sensor (Fig. 1) is a stack of five cylindrical solid state silicon detectors surrounded by an anticoincidence shield of plastic scintillator and a sixth silicon detector to distinguish between absorption and penetration mode. The two first thinner detectors are divided in six sectors to allow a rough trajectory determination and particle range corrections, which improve isotopic discrimination for light nuclei. Nominal energy range for electrons is 250 keV to 10 MeV and for hydrogen and helium nuclei from 4 to 53 MeV/n. EPHIN is located onboard SOHO spacecraft, in a halo orbit around lagrangian point L1, outside the influence of Earth magnetosphere. The sensor axis points permanently in the direction of the nominal interplanetary magnetic field at 1 AU, 45º west of the spacecraft-Sun line. A detailed description of the sensor can be found in Müller- Mellin et al (1995). Fig. 1. EPHIN sensor