Hypothetical signals beyond the primary ISN He flow as perspective targets for IMAP
Thursday, 17 December 2015
Poster Hall (Moscone South)
Interstellar Boundary Explorer (IBEX) is a small Earth-orbiting spacecraft that successfully investigates the local interstellar medium that surrounds heliosphere. The IBEX-Lo sensor samples the primary population of interstellar neutral (ISN) helium with a high signal-to-noise ratio. In addition to this strong signal, which has been interpreted as a Maxwell-Boltzmann distribution of the ISN gas in front of heliosphere, the observations also revealed elevated wings above the background level both in longitude and latitude. This signal, dubbed the a Warm Breeze, is likely the secondary population of ISN He created in the outer heliosheath. In addition, IBEX sees an unexplained ubiquitous background in the lowest energy channels. In this study, we hypothesize departures from the assumptions adopted so far in the data interpretation that could solve remaining unexplained features in the IBEX data or may be pursued by future IMAP mission. We show that the Warm Breeze cannot be explained by a kappa distribution function of the ISN He source. We identify regions in the sky where signatures of the hypothetical kappa distribution of the ISN He atoms would show up. We speculate that the temperature of ISN He in front of the heliosphere is not isotropic and simulate the expected signatures of this anisotropy in the IBEX-Lo signal to identify the regions in the sky that are the most promising to analyze. We compare these results of the study with the IBEX detection capabilities and find that due to its very high signal-to-noise ratio IBEX would be able to see the indicators of the studied scenarios. However, its location close to the magnetosphere and its energy sensitivity threshold makes the discovery very challenging. We specify requirements for IMAP needed to discover the hypothesized departures of the ISN distribution function from standard assumptions and thus allowing a detailed study of plasma-neutral coupling processes in the interstellar medium.