Observation by Ulysses of hot (∼270 keV) coronal particles at 32° south heliolatitude and 4.6 AU

Abstract

An unusual event of streaming 60 keV‐2 MeV ions (with energy spectrum peaked ∼270 keV) and of 42–315 keV electrons occurred during the passage of a coronal mass ejection (CME) over the Ulysses spacecraft June 9–13, 1993, located at helioradius 4.6 AU and heliolatitude 32° south. The topology of the interplanetary magnetic field (IMF) within the CME has been identified as a helical magnetic flux rope by Gosling et al. [1994]. The ion and electron pitch angle distributions (PADs) had a bidirectional component in the outer (large‐pitch) regions of the flux rope, while there were strongly unidirectional (antisunward) beams in the inner (small‐pitch) core of the structure, where the electron PADs also displayed a distinctive depletion of electrons moving inward (sunward). Because the core ion beam was narrow, we can associate the observed energy spectrum in the peak direction of the beam (characterized by a Maxwellian with kT = 270 keV) directly with the spectrum injected in the inner heliosphere. The well‐defined spatial structure of the event and the absence of any clear signatures of local interplanetary shock acceleration during the period June 9–17 implies that the injection source could have been a long‐lived hot coronal ion population. The “weak scattering” electron PAD implies that the other (antisunward) end of the core of the flux rope was magnetically connected, not back to the sun, but rather to the outer heliosphere.