The calc_photon_flux function calculates the unconvolved source
or background model photon flux for all or a portion of a
source or background data set by data ID or background ID. A
subset of the model can be specified by entering the low and
high ends of the desired data interval in units of keV for energy
data or Angstroms for wavelength data. To calculate the energy
flux for an unconvolved source or background model, the
function calc_energy_flux can be used by data ID or background ID.
-
lo - low limit;
default=None
-
hi - high limit;
default=None
-
id - data ID;
if not given, uses the default sherpa id (id=1 by default, see "ahelp get_default_id")
-
bkg_id - background data ID
The calc_photon_flux function can be called with no
arguments, in which case the unconvolved model photon flux
will be calculated over the entire data range of the
default data set. The photon flux of an unconvolved
background model can be integrated by
supplying the corresponding Sherpa-assigned background ID
as the argument (e.g. "1" or "2" for the first or second
background data set automatically
located by Sherpa in the corresponding source data set).
For 1-D data, if:
o) one energy (or wavelength) is given (as opposed to a
[lo, hi] interval), then the photon flux of the
unconvolved model at
that energy (or wavelength) is returned in units of
photons/cm^2/sec/keV (or photons/cm^2/sec/A).
o) an energy or wavelength range is given with the 'lo' and 'hi'
arguments, then the total integrated photon flux over the given
range is returned in units of photons/cm^2/sec.
o) no value or range is specified, then the total integrated photon
flux over the full range of the dataset is returned in units of
photons/cm^2/sec.
For 1-D data, if an instrument model is not used, the units are
assumed to be counts, or counts per bin-width. See the
Note on Units below.
For 2-D data the total integrated photon flux is carried out over
the entire input image.
Note on Units: In its current incarnation, Sherpa has no explicit
knowledge of data or model units. The units displayed with computed
fluxes are defaults, generally correct for standard analyses of 1-D PHA
energy/wavelength spectra (XSPEC-like analyses). They may be incorrect
for non-standard analyses, or for analyses of 2-D spatial images with
exposure maps, etc. The correct units can be determined by working
backwards from the data, taking into account the exposure time, the
units of the instrument model, the bin units, etc.
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