Observations and Simulations of the Ribbon at IBEX-Lo Energies (~0.2–0.9 keV)

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Abstract We present simulations of the Interstellar Boundary Explorer (IBEX) ribbon at ∼0.2–0.9 keV for comparison with IBEX-Lo observations. Past ribbon studies have mainly focused on IBEX-Hi energies (∼0.7–4.3 keV), where the ribbon is most visible in the sky. Here, we utilize the model from E. J. Zirnstein et al. (2023), with updated solar wind (SW) conditions from interplanetary scintillation observations, to determine the variation of the ribbon at energies as low as ∼0.2 keV and reproduce the intensity of the observations seen at ∼0.4 and ∼0.9 keV. First, we show results by separating the signal by its neutral SW (NSW) source and neutral interstellar pickup ion (NPUI) source, showing that the NPUI source dominates the ribbon signal at ∼0.2 keV from 2009 to 2018, and the NSW source begins increasing at high latitudes after 2018. At ∼0.4 keV and ∼0.9 keV, the NSW source of the ribbon dominates the intensities at all times and locations. Next, we compare to IBEX-Lo observations averaging over multiyear intervals from 2009 to 2019. The ribbon model significantly underestimates the observations at ∼0.2 keV at all times, suggesting there is no ribbon, but also suggesting that neutralized heliosheath ions are important at low energies for the ribbon source, which are not currently included in our model. At ∼0.4 keV, the model comparisons with data improve, especially for the 2017–2019 period. Finally, at ∼0.9 keV, our model approximately reproduces the intensity of the observed ribbon at all times, although slightly overestimating the intensities from 2013 to 2019.

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