Authors: H. Islam, F. Rahmanifard, N. A. Schwadron, E. Möbius (University of New Hampshire)

The Interstellar Boundary Explorer (IBEX) mission investigates the very local interstellar medium (VLISM) and its interaction with our heliosphere through sampling of Interstellar neutral )ISN( atoms ) a few 10s to several 100s of eV) and energetic neutral atoms (ENAs, 0.2 – 6 keV). Over 12 years of IBEX observations have provided the opportunity to monitor this interaction through different phases of solar activity. Among the VLISM constituents, ISN He is the least affected by ionization processes at the heliospheric boundary and inside the heliosphere. Therefore, the growing ISN He dataset provides an unprecedented opportunity to advance our knowledge of the parameters that describe the motion of the Sun through the VLISM (velocity vector and temperature). On the other hand, a large fraction of ISN H is ionized inside the heliosphere and their trajectories are strongly affected by radiation pressure, which both vary with solar activity.

In this study, we provide count rates and exposure time maps that include the sputtering and charge-exchange contributions of ISN H and He based on a good-time list for each year as a function of orbit and spin angle for energy steps (E-Steps) 2 (center energy 29 eV) and 3 (center energy 55 eV) throughout the full solar cycle 24 (2009–2020). While the maps from E-Step 3 mainly result from sputtering by ISN He, E-Step 2 rates include the contributions of charge exchange for ISN H and sputtering by ISN He. We correct these maps for throughput reductions associated with electronic deadtime, and for a pointing offset that occurred after 2016. The dataset associated with these maps is being prepared for release to the science community. These maps and the associated dataset provide (1) a scientific opportunity to further investigate the sources and properties of interstellar neutral atoms and how they are affected by variations in solar activity (2) a compact, visualized format for interstellar neutral atom data in preparation for future data to be returned by the Interstellar Mapping and Acceleration Probe mission.

We are extending this study by the parameter estimation of Interstellar Helium by comparing the observed rates  with rates obtain from simulation. We are using same methodology used by Schwadron et. al.(2016) for derivation of oxygen parameters. For forward modeling a full integration model is used where the complete IBEX-Lo response function in the spacecraft frame of reference is numerically integrated to obtain rates. This method differs from adopting closed form solution in the Earth frame of reference which has developed by Lee et.al (2012) and implemented by Möbius et.al (2012). This is the first study where we are analyzing  simultaneous effect of primary and secondary population  for chi-square minimization without any assumptions. This is a work on progress.