Spectral Evolution of Anomalous Cosmic Rays at Voyager 1 Beyond the Termination Shock

Monday, 15 December 2014
Udara K Senanayake, University of Alabama in Huntsville, Physics / Space Science, Huntsville, AL, United States, Vladimir A Florinski, University of Alabama in Huntsville, Huntsville, AL, United States, Alan C Cummings, CALTECH, Pasadena, CA, United States and Edward C Stone, California Institute of Technology, Pasadena, CA, United States
When Voyager 1 spacecraft crossed the termination shock on 16th December 2004, the energy spectra of anomalous cosmic rays (ACRs) could not have been produced by steady state diffusive shock acceleration. However, over the next few years, in the declining phase of the solar cycle, the spectra began to evolve into the expected power-law profile. Energetic particle transport coefficients, such as diffusion and drift, and also ACR source strength tend to increase with declining levels of solar activity. In this work, we propose that the solar cycle had an important effect on the “unrolling” spectra in the heliosheath at Voyager 1. To investigate the spectral evolution of ACRs, a magentohydrodynamic background model with stationary solar-wind inner boundary conditions will be used to model the transport of helium and oxygen ions. We use a backward-in- time stochastic integration technique where phase-space trajectories are integrated until the so called “injection energy” is reached. Our simulation results will be compared with Voyager 1 observations from 2005 to 2012.