calc_photon_flux¶

sherpa.astro.ui.calc_photon_flux(lo=None, hi=None, id=None, bkg_id=None)¶

Integrate the source model over a pass band.

Calculate the integral of S(E) over a pass band, where S(E) is the spectral model evaluated for each bin (that is, the model without any instrumental responses applied to it).

Parameters:	lo (number, optional) – The minimum limit of the band. Use `None`, the default, to use the low value of the data set. hi (number, optional) – The maximum limit of the band, which must be larger than lo. Use `None`, the default, to use the upper value of the data set. id (int or str, optional) – Use the source expression associated with this data set. If not given then the default identifier is used, as returned by get_default_id. bkg_id (int or str, optional) – If set, use the model associated with the given background component rather than the source model.
Returns:	The flux from the source model integrated over the given band. This represents the flux from the model without any instrument response (i.e. the intrinsic flux of the source). For X-Spec style models the units will be photon/cm^2/s. If hi is `None` but lo is set the the flux density is returned at that point: photon/cm^2/s/keV or photon/cm^2/s/Angstrom depending on the analysis setting.
Return type:	number

See also

calc_data_sum(): Sum up the observed counts over a pass band.
calc_model_sum(): Sum up the fitted model over a pass band.
calc_energy_flux(): Integrate the source model over a pass band.
calc_source_sum(): Sum up the source model over a pass band.
set_analysis(): Set the units used when fitting and displaying spectral data
set_model(): Set the source model expression for a data set.

Notes

The units of lo and hi are determined by the analysis setting for the data set (e.g. get_analysis).

Any existing filter on the data set - e.g. as created by ignore or notice - is ignored by this function.

The flux is calculated from the given source model, so if it includes an absorbing component then the result will represent the absorbed flux. The absorbing component can be removed, or set to absorb no photons, to get the un-absorbed flux.

The units of the answer depend on the model components used in the source expression and the axis or axes of the data set. It is unlikely to give sensible results for 2D data sets.

Examples

Calculate the photon flux over the ranges 0.5 to 2 and 0.5 to 7 keV, and compared to the energy fluxes for the same bands:

>>> set_analysis('energy')
>>> calc_photon_flux(0.5, 2)
0.35190275
>>> calc_photon_flux(0.5, 7)
0.49050927
>>> calc_energy_flux(0.5, 2)
5.7224906878061796e-10
>>> calc_energy_flux(0.5, 7)
1.3758131915063825e-09

Calculate the photon flux density at 0.5 keV for the source “core”:

>>> calc_photon_flux(0.5, id="core")
0.64978176