General notes: (1) units used: eV, cm, sr, s (2) lines beginning with '#' are comments in all files. (3) this response function is valid for (neutral) atomic hydrogen and does not apply to heavier species. The response of IBEX-Hi to neutral flux is split into angular response (coll_resp_theta_phi30.txt), energy response (T_energies.txt, T_triples.txt), and overall efficiency (E_centre.txt, G_values.txt). Files ===== coll_resp_theta_phi30.txt ------------------------- The angular response of IBEX-Hi is taken to be that of its collimator; we ignore the slight energy-dependent angular variation of ESA acceptance in calculating the response function. This file has long integers, from a Monte Carlo simulation, in an array, and it needs pre-processing before it is directly useful. The array is defined in spherical coordinates based on the collimator axis of symmetry (i.e., perpendicular to the entrance plane of IBEX-Hi). The rows correspond to theta (polar) ranges covering from 0 to 9 degrees in 0.2 degree steps; the columns correspond to phi ranges (azimuthal) covering from 0 to 30 degrees in 1 degree steps. There is no need to go beyond 30 degrees; due to the hexagonal symmetry of the collimator, any azimuthal angle can be mapped into this range. Phi == 0 corresponds to about -35 degrees with respect to the spacecraft x axis, in the plane of the collimator face. Before this file can be used, each entry must be scaled by its solid angle (which goes as 1/sin(theta)); then, the response overall must be normalized to integrate to 1 over all solid angle (which is 12 times the integral over the supplied 0 <= phi <= 30 degree range). Note that there is negligible error introduced by averaging over phi response and assuming a cylindrically symmetric response for IBEX-Hi. E_centre.txt ------------ 6 numbers, one per line, corresponding to the central energy in eV of the 6 IBEX-Hi bandpasses (associated with the 6 ESA settings). "Central energy" is not a uniquely defined value; the numbers in this file are to be used with the rest of the response function files. G_values.txt ------------ 6 numbers, one per line, corresponding to the geometric factor, in cm^2 sr eV, for the 6 IBEX-Hi bandpasses (associated with the 6 ESA settings), for qualified triple events. T_energies.txt T_triples.txt ------------- These two files go together. Both have 6 columns, corresponding to the 6 ESA settings of IBEX-Hi. Each column of T_energies.txt is a list of energies, in eV. The corresponding entries in the corresponding column of T_triples.txt give the response of IBEX-Hi, normalized such that the integral over energy per ESA setting is 1 (dE is the energy spacing between points in T_energies). IBEX-Hi response should be linearly interpolated between points and taken to be 0 outside the endpoints. Use === For a flux of N particles / eV / sr / cm^2 / s, IBEX-Hi at a given ESA setting will see a rate given by the integral over energy and solid angle of N * collimator response(theta, phi) * G_value(depends on ESA) * T_triple(ESA, energy). (Note that E_central only comes into play if you've divided the values in G_values.txt by it to get G in units of cm^2 sr eV/eV; if you've done this, you need to multiply by E_central again.) Under the approximations of isotropic flux and of minimal variation of the flux with energy over a given bandpass, the (normalized) collimator response and the (normalized) energy response integrate to 1, leaving the simpler formula N * G_value(ESA).