Voyager Observations of Anomalous Cosmic Rays in the Outer Heliosphere

摘要

The intensity of anomalous cosmic rays (ACRs) at Voyager 1 (V1) and Voyager 2 (V2), now both in the heliosheath, have recently exhibited intriguing changes. At V1, the ACR He and O intensities have plateaued and are declining. If the decline is due to particles leaking out through the heliopause, then the V1 spacecraft may be close to entering interstellar space for the first time. At V2, the ACR He and O intensities have begun to rapidly increase and at several energies now exceed the intensities at V1, suggesting that the ACR source intensity in the southern part of the heliosphere is greater than that in the north, or that the source of ACRs is along the flank or tail of the heliosphere. In deriving the ACR intensities we find that the energy spectrum of the low-energy particles, which are accelerated at the termination shock, the Termination Shock Particles, have a double-power-law shape rather than the generally expected power-law at low energies with an exponential roll-over at higher energies.