Interstellar hydrogen fluxes measured by IBEX-Lo in 2009: numerical modeling and comparison with the data

Abstract

In this paper, we perform numerical modeling of the interstellar hydrogen fluxes measured by IBEX-Lo during orbit 23 (spring 2009) using a state-of-the-art kinetic model of the interstellar neutral hydrogen distribution in the heliosphere. This model takes into account the temporal and heliolatitudinal variations of the solar parameters as well as non-Maxwellian kinetic properties of the hydrogen distribution due to charge exchange in the heliospheric interface. We found that there is a qualitative difference between the IBEX-Lo data and the modeling results obtained with the three-dimensional, time-dependent model. Namely, the model predicts a larger count rate in energy bin~2 (20-41 eV) than in energy bin~1 (11-21 eV), while the data shows the opposite case. We perform study of the model parameter effects on the IBEX-Lo fluxes and the ratio of fluxes in two energy channels. We shown that the most important parameter, which has a major influence on the ratio of the fluxes in the two energy bins, is the solar radiation pressure. The parameter fitting procedure shows that the best agreement between the model result and the data occurs in the case when the ratio of the solar radiation pressure to the solar gravitation, ${\mu }_0$, is 1.26${}_{-0.076}^{+0.06}$, and the total ionization rate of hydrogen at 1 AU is ${\beta }_{E,0}=3.7_{-0.35}^{+0.39}\times 10^{-7}$~s${}^{-1}$. We have found that the value of ${\mu }_0$ is much larger than ${\mu }_0=0.89$, which is the value derived from the integrated solar Lyman-alpha flux data for the period of time studied. We discuss possible reasons for the differences.

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• Evolution of the Solar Lyman-Alpha line profile during the solar cycle
• Interstellar neutral helium in the heliosphere from IBEX observations. V. Observations in IBEX-Lo ESA steps 1, 2, & 3
• Very Local Interstellar Medium Revealed by Complete Solar Cycle of Interstellar Neutral Helium Observations with IBEX
• Heliospheric Energetic Neutral Atoms: Non-stationary Modeling and Comparison with IBEX-Hi data
• Evolution of the solar Ly-$\alpha$ line profile during the solar cycle. II. How accurate is the present radiation pressure paradigm for interstellar neutral H in the heliosphere?
• Angular Scattering in Charge Exchange: Issues and Implications for Secondary Interstellar Hydrogen
• Effects of dispersion of the dust velocity in the LISM on the interstellar dust distribution inside the heliosphere
• Backscattered solar Lyman-alpha emission as a tool for the heliospheric boundary exploration
• Absorption of the Lyman-$\alpha$ radiation in the heliosphere
• Understanding the IBEX ribbon using the kinetic model of pickup proton transport in a scatter-free limit