Temporal Variation of Heliospheric ENAs (~5-15keV) from 2007-2010 measured by STE-D

Energetic Neutral Atoms (ENAs) produced in the boundary regions of the heliosphere provide information about the interaction between the heliosphere and the local interstellar medium. The Suprathermal Electron (STE) instrument on the STEREO mission has measured ~5-15 keV ENAs during 2007-2008, coming from the outer heliosphere between ~255° and ~280° ecliptic longitude, with a maximum flux occurring around 265°, after removing the contribution from suprathermal electrons and galactic x-ray fluxes. These ENA emissions are consistent with the narrow ribbon of enhanced ENA fluxes observed at 4.3 keV by IBEX, while they have narrower angular width and lower fluxes compared to the broad belt of ENAs observed at ~5-55 keV by Cassini. In this study we will compare the ~5-15 keV ENAs observed by STE during 2007-2010 and discuss their temporal variation.