Inferring the IBEX ribbon shape from ENA temporal variations: A proof-of-concept for IMAP observations

Abstract:

Since its discovery in 2009, the shape of the IBEX ENA ribbon has been a subject of numerous studies. It appearsat energies ~0.2-6 keV and is most pronounced at ~1 keV. It is almost circular (wrapping ~300° across the sky), narrow (~20°-40° depending on energy), and its center lies near BLISM, whose field lines are draped around the heliosphere. The ribbon intensity is ~2 to 3 times higher than the more diffuse globally distributed flux (GDF) and varies on time scales that are longer than the underlying GDF.

Eleven years into the mission, the transverse shape of the ribbon has not yet been resolved; partially for reasons inherent to the data resolution, and the fact that the ribbon changes with time and direction in the sky. We present a novel method to infer the actual transverse shape of the ribbon using sequential time variations of ENA fluxes, with no modeling assumptions involved. The method utilizes the difference in temporal evolution between the ribbon and GDF fluxes. We then use the inferred shape to statistically quantify the GDF contributionto the observed ribbon intensity.

This ribbon separation method works best at higher angular resolutions and improved counting statistics, when there are large gradual changesin the solar wind. Results thus provide a proof-of-concept that can be applied on IMAP ENA measurements in the future.