Sudden intensity increases and radial gradient changes of cosmic ray MeV electrons and protons observed at Voyager 1 beyond 111 AU in the heliosheath

Abstract

Voyager 1 has entered regions of different propagation conditions for energetic cosmic rays in the outer heliosheath at a distance of about 111 AU from the Sun. The low energy 6–14 MeV galactic electron intensity increased by ~20% over a time period ≤10 days and the electron radial intensity gradient abruptly decreased from ∼19%/AU to ∼8%/AU at 2009.7 at a radial distance of 111.2 AU. At about 2011.2 at a distance of 116.6 AU a second abrupt intensity increase of ∼25% was observed for electrons. After the second sudden electron increase the radial intensity gradient increased to 18%/AU. This large positive gradient and the ∼13 day periodic variations of >200 MeV particles observed near the end of 2011 indicate that V1 is still within the overall heliospheric modulating region. The implications of these results regarding the proximity of the heliopause are discussed.