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).