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Distance to the IBEX Ribbon Source Inferred from Parallax

Maps of Energetic Neutral Atom (ENA) fluxes obtained from Interstellar Boundary Explorer (IBEX) observations revealed a bright structure extending over the sky, subsequently dubbed the IBEX ribbon. The ribbon had not been expected from the existing models and theories prior to IBEX, and a number of mechanisms have since been proposed to explain the observations. In these mechanisms, the observed ENAs emerge from source plasmas located at different distances from the Sun. Since each part of the sky is observed by IBEX twice during the year from opposite sides of the Sun, the apparent position of the ribbon as observed in the sky is shifted due to parallax. To determine the ribbon parallax, we found the precise location of the maximum signal of the ribbon observed in each orbital arc. The obtained apparent positions were subsequently corrected for the Compton-Getting effect, gravitational deflection, and radiation pressure. Finally, we selected a part of the ribbon where its position is similar between the IBEX energy passbands. We compared the apparent positions obtained from the viewing locations on the opposite sides of the Sun, and found that they are shifted by a parallax angle of $0.41^\circ\pm0.15^\circ$, which corresponds to a distance of $140^{+84}_{-38}$ AU. This finding supports models of the ribbon with the source located just outside the heliopause.