Voyager SSG November 3-4, 2011 F.B. McDonald 1, A.C. Cummings 2, E.C. Stone 2, B.C. Heikkila 3, N. Lal 3, W.R. Webber 4 1 Institute for Physical Science and Technology, Univ. of Maryland, College Park, MD, USA 2 California Institute of Technology, Pasadena, CA, USA 3 NASA/Goddard Space Flight Center, Greenbelt, MD, USA 4 Dept. of Physics and Astronomy, New Mexico State Univ., Las Cruces, New Mexico, USA Voyager Observations of Cosmic Rays in the Heliosheath

Voyager Cosmic Ray Telescopes Energetic Particle Coverage H: MeV He: MeV/n Z = 1-28 (Resolves Isotopes) E: 2.5 – 160 MeV Outline 1.Introduction 2.What’s up at 1 AU! 3.Galactic Cosmic Rays in the Heliosheath. 4.Long-lasting Heliosheath Intensity Increases 5.Discussion ← 28.6 cm →

Introduction

IPB is 28% below the previous minima of cycles Heliospheric neutral current sheet approaches minimum value at a slower rate than previously observed. Wang, Robbrecht and Sheely (2009) have pointed out that these effects appear to be related – the weaker polar fields result in the apparent refusal of the heliospheric current sheet to flatten closer to the equator.

– a)6.4% / year (V1) G D = 1.8 % / AU ( ) g r = 0.6 % / year b)11.6 % / year (V1) G D = 3.2 % / AU (2010.0) g r = 1.2 % / year The “decrease in the V2 intensities between – 2011 is an artifact created by the long lasting transient increases peaking in late 2008 and There is a significant radial gradient for GCR H and He.

– : 60 % / year (V1) G D = 16.6 % / AU (2010.0) g r = 14.6 % / year

1 AU Comparison

GCR Electrons MeV Origin: Knock-on electrons Directly accelerated primaries Interstellar secondaries from the decay of charged pions The interstellar spectrum can be determined directly from the shape of the VLF galactic polar radio spectrum via synchrotron formula for electron motion in the galactic magnetic fields Webber and Higbie have recalculated the interstellar electron spectrum based on work by Vladimir Ptuskin et al, 2006 on the diffusion of galactic cosmic rays in the interstellar medium

Electron Spectra

HELIOSHEATH TRANSIENT INCREASES

Arrows define discontinuous changes in the 10MeV electron intensity. Note that the rate of increase appears to be approximately the same in alternate regions.

Stone, et. al,., 2011; Burlaga and Ness, 2010

Arrows Mark Voyager-1 Events

Discussion At V1 significant variability in all components from TSX to ~ Then relatively smooth, exponential increases in GCRs Long lived TSP events previously noted as V1 (and V2) neared the TS. They appear to represent periods when the spacecraft is magnetically connected to the TS. The 2 modest jumps in V1 electron intensity at and represent passage into a different magnet field regime. The V2 long lasting, transient increases probably also reflect connections to a different regime of the heliosheath. The C low energy J=AT slope is consistent with the concept advanced by Florinski and Pogorelov (2008) that the heliosheath is a long term storage region for GCRs < ~ 200MeV/n. The flat time history of V1 GCR He > 265 MeV/n and the decrease in V1 ACR and TSP intensities may suggest V1 is approaching the heliopause. The End Is Near!!!