An ACR Mediated Termination Shock

The Voyager 2 crossing of the termination shock indicated that most of the energy from the thermal solar wind ions was transferred to pickup ions (PUIs) and other energetic particles at the shock (Richardson et al. 2008). Here, following the work of Gkiouldiou et al. (2022), we use hybrid simulations at the termination shock for the Voyager 2, flank, and tail directions from Giacalone et al. (2021) to evaluate the distributions of different ion species at the shock over the energy range of 0.52 to 55 keV. As an update to Gkioulidou et al. (2022), we include the contribution from accelerated particles that are shown to be important and mediate the termination shock (Florinski et al. 2010) as distinct from reflected PUIs. We model thermal solar wind ions, transmitted PUIs, and reflected PUIs with Maxwellian distributions, and an accelerated PUI population via power law distributions. We find that the hybrid model indicates a population of anomalous cosmic rays (ACRs) is derived from the acceleration of reflected PUIs, which have an energy density of 23% in the Voyager 2 direction. Extrapolating these ion distributions to all directions, we perform global ENA modeling of the heliosphere in the IBEX-Hi and INCA energy range using an MHD model with solar minimum conditions for the solar wind and a neutral hydrogen density of nH=0.18 cm-3 in the ISM, which is compatible with results from Swaczyna et al. (2020). We find that the scaling factor (roughly a factor of 2) used by prior modeling works to quantitatively compare with IBEX-Hi observations (Zirnstein et al. 2017; Kornbleuth et al. 2021) is no longer required at energies up to 2.73 keV due to the inclusion of a separate accelerated PUI population. The gap between predicted ENAs and observed ENAs in the 4.29 keV channel of IBEX and at INCA energies still exists, and a spectral break is required to match the higher energies of INCA.