Higher‐energy plasma ions found near the termination shock: Analyses of Voyager 2 data in the heliosheath and in the outer heliosphere

Abstract

We have found in the Voyager 2 (V2) plasma science data in the heliosheath (HS) near the termination shock (TS) high‐energy ions (HEIs) in addition to the bulk plasma convective flow ions. The HEI detections temporally coincide with increased V2 plasma wave subsystem (PWS) activity in “event A” of Gurnett and Kurth (2008). Maxwellian fits to HEI detections indicate the HEIs are moving radially anti‐Sunward with a proton speed of 600 km/s, a density of 10−4 cm−3, and a thermal speed of 10 km/s. The heliosheath bulk convective protons have a speed of 204 km/s, a density of 0.0029 cm−3, and a thermal speed of 26.7 km/s. The HEI flux and ram pressure are approximately 10% and 30% of those of the bulk HS flow. Since the HEI speed is both close to twice the solar wind speed and independent of the heliosheath bulk plasma speed, the HEIs may be detections of pickup protons formed in the solar wind and convected through the TS. The HEIs also are reminiscent of the pickup protons upstream of the Mars bow shock where their energy also was independent of the bulk plasma speed and attributed to multiple reflections off the Mars bow shock. Gurnett and Kurth's (2008) event A enhanced PWS activity may be generated by a two‐stream instability from the interaction of these HEIs with the heliosheath bulk plasma ions. We present our findings, discuss their implications, and also present alternative interpretations.