2009ApJ...694L..79H

We present an alternate interpretation of recent STEREO/STE observations which were attributed to energetic neutral atoms (ENAs) from the heliosheath. The inferred ENA intensities, as a function of longitude, are very similar to the instrument response, implying that the source or sources are quite narrow. Such narrow sources may be quite difficult to ascribe to the available sources of ENAs, such as the charge exchange of energetic charged particles with ambient neutrals, which tend to be much broader. We point out that the largest intensity maximum observed by STEREO/STE is centered at the same ecliptic longitude as the brightest known X-ray source, Sco X-1. If this is indeed the source of the detected flux, it naturally accounts for the small source width. We find that the observed energy spectrum and intensity are also consistent with the X-rays from Sco X-1. If this interpretation is correct, then observers must take care in analyzing ENA data based on detectors sensitive to radiation other than ENAs. The problem of energy dissipation in the solar wind termination shock remains unsolved, while current understanding of the interaction between the solar wind and interstellar wind awaits future observations.