When XPOSE is run, a window will be created with a number of input
items. Here is a description of each input item.
Coordinate System
The user must specify whether galactic or
celestial coordinates will be used.
Coordinates
The coordinates of the source point may be entered in
either in decimal degree measure or
hours-minutes-seconds/degrees-minutes-seconds.
Start and End Times
The start and end times for the exposure calculation may be entered either as decimal Truncated Julian Dates or in
Gregorian fashion. The
time range need not be restricted to within a given viewing period.
The program is capable of processing any time range corresponding to the
instrument lifetime as long as the 50 viewing period limit is not exceeded.
Output Filename
The output filename is used to name the output
binary files. The binary files are named by appending the applicable
energy level number to this string.
Acceptance Angle (deg)
This parameter is used to determine which
viewing periods will be processed within the specified time range. All viewing
periods that have pointing directions within this acceptance angle from the
specified source point will be included in the calculation.
Event Class
One may select between calibration files utilizing all
events or only class A events. The default is for all events.
Scale Type Toggle
If the automatic setting is specified,
the scale factors
are extracted from
$EGRET_PROGRAMS/sequence/scale.factor
Otherwise, the
user must specify the scale factor manually. This factor is provided to
adjust for variation of instrument sensitivity over extended periods of time.
Zenith Cutoff Toggle
If automatic is selected, the program will
automatically determine an appropriate zenith cutoff angle based upon the
lower energy bound of the range. The return or tab keys must be pressed
when entering the energy ranges in order to prompt the calculation. If the
toggle is set to manual, the cutoff angles must be provided for every energy
level active in order to execute the program.
Energy Level Slider
This slider allows the user to specify the
number of energy levels to be calculated. As the number of levels is
increased, the panel items associated with them become active and ready
for input.
Energy Ranges
Energy bounds must be provided for every active level.
Energies are to be in MeV.
Zenith Cutoff Angles
The zenith cutoff angles represent the full
angular width of an rejection cone. If the earth is found to be within
this cone, whose axis is determined by the pointing direction,
during a small time interval, the livetime associated
with the interval is disregarded.
Spectral Indices
Spectral indices are used for energy-weighting
in the calculation of sensitive areas. If possible, one should attempt to
match the spectral index of the source with that used in the exposure
calculation. The value 2.1 is chosen as a default.
In the input panel two means of listing viewing period start times are
provided. One may list all the viewing periods with their respective
TJD start times by pressing the "<List All Viewing Periods>" button.
Once source coordinates have been entered (and the return key pressed), the
"<Viewing Periods near Position>" button will become active. Upon
pressing it, a pop-up window will appear and display the viewing periods
with pointing direction less than the "Include Viewing Periods within"
parameter away from the source. The TJD start and end times are displayed, as
well as the number of degrees off axis.
