For each of the 19 orbits in this release, there are five ENA skymaps of the magnetosphere as well as the five underlying ASCII count files, corresponding to ENA measurements at ~0.71, ~1.11, ~1.74, ~2.73, and ~4.3 keV. Each count file contains a descriptive header.
This data release comprises 19 orbits that cover nightside and dayside viewing by IBEX.
For each orbit, there are 5 ENA skymaps as well as 5 ASCII files, corresponding to ENA measurements at ~0.71, ~1.11, ~1.74, ~2.73, and ~4.3 keV.
The data are arranged in 6-degree bins in the spin phase (for each spin, there are 60 6-degree bins covering the 360 degree view).
Each data file includes timing, spacecraft and object ephemeris, and spacecraft pointing information along with the ENA skymap time vs Counts in 6-degree bins covering 360 degrees. ENA counts are binned every 96 spins (~24 minutes) over the whole sky).
The magnetospheric images are created using the ephemeris and pointing information to project the measured ENAs onto the XZ plane.
Converting Counts to Fluxes
The ENA flux J(E) at the energy E can be derived from the count rate C using the following formula: JENA (E)=C/ετEG, where G is the geometric factor for each energy band, ε is the sensor efficiency, and τ is the effective accumulation time.
G, ε, and τ are given by Funsten et al. (2009).
Τ is the time when the sensor was pointing at the region of interest.
ENA and ion fluxes are related by:
where is the observed ENA flux projected in GSE XZ plane, is the local ion flux, and is the energy-dependent charge-exchange cross section between energetic proton and ambient hydrogen atoms (), calculated from an empirical formula (Lindsay and Stebbings, 2005).
nH can be calculated based on empirical models such as a spherical harmonics model obtained by the TWINS1-LAD measurement assuming isotropic Lyman-α resonant scattering (Zoennchen et al., 2011).
IBEX Magnetospheric Imaging Considerations
Spacial/temporal variationsi - IBEX instruments have large FOVs, and hence poor spatial resolution (~2 to ~5 RE along the XGSE and sub-RE in the ZGSE direction) at any given instant and place where the FOV intersects the XZ meridian plane. Also the spacecraft location and spin axis are not fixed with respect to the Earth and therefore the viewing perspective slowly changes with time. Therefor when creating composite images of the magnetosphere, certain assumptions must be made with respect to the expected ENA emission spatial gradients within the magnetosphere, and the expected time scales of temporal variations across these spatial scales.
Line-of-sight integration - The data for this release is presented under the assumption that most of the ENA emissions occur within the magnetosphere and peaks in the noon-midnight meridian plane, which may not always be the case. This complication is true of all imaging of optically thin environments.
Geocorona - The density of the geocorona is assumed to fall of radially with geocentric distance, which is likely an oversimplification.
Pitch angle variations - Since ENA emissions are assumed to peak near the noon-midnight meridian plane, pitch angles must be close to 90° between the magnetospheric magnetic field and the IBEX instrument field of views, however there may actually be some pitch angle dependencies on ENA emissions that are not considered.