Calculates the unconvolved energy flux for source or background datasets.
sherpa> [B]EFLUX [# [ID]] [{(<value>) | (<min>:<max>) | (<region
descriptor>)} ] \
[ {(<model component>) | (<model stack>)} ]
EFLUX is used for computing source energy fluxes, while BEFLUX is used
for computing background energy fluxes.
# specifies the dataset over which the source model is evaluated. The
ID modifier is used only for computing background fluxes, and then if
and only if the Sherpa state object variable multiback is set to 1,
i.e., if more than one background dataset is to be associated with a
single source dataset. The ID modifier may be any unreserved string
(e.g., A, foo, etc.), i.e., a string that is not a parsable command.
The default is to compute energy fluxes for all appropriate datasets
(i.e., those for which source/background expressions have been
defined). The flux may be computed at one energy/wavelength, over a
range of energies/wavelengths, or within a 2-D region, with the default
being to compute the flux the total available range.
The flux may also be computed for individual model components, or for
previously defined model stacks, with the default being to compute the
flux using all model components in the SOURCE or BACKGROUND expression.
A source or background model stack
must be defined before a respective flux can be computed; see the SOURCE
and BACKGROUND commands.
This is true even if one computes the flux of an individual model
component or of models defined in a model stack. (This limitation
will be removed in a future version of Sherpa.)
For 1-D data, if:
-
one energy (or wavelength) <value> is given,
then the energy flux at that energy (or wavelength) is returned in units of
ergs/cm^2/sec/keV
(or ergs/cm^2/sec/A).
-
an energy or wavelength range is given with the
<min> and <max> arguments, then
the total integrated energy flux over the given range is returned in units of
ergs/cm^2/sec.
-
no value or range is
specified, then the total integrated energy flux over the full range
of the dataset is returned in units of
ergs/cm^2/sec.
For 1-D data, if an instrument model is not used, the units are
(perhaps incorrectly) assumed to be counts, or counts per bin-width.
See the Note on Units below.
For 2-D data, if a region descriptor is given, then
the total integrated energy flux within that region is returned;
otherwise, the integration 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.
Tip: To perform background subtraction in
Sherpa, the command SUBTRACT must be issued; this
is in contrast to XSPEC, which performs background
subtraction automatically.
The energy flux may be computed using the Sherpa/S-Lang module
functions
get_eflux and
get_beflux.
Calculate the integrated energy flux over the full energy range:
sherpa> EFLUX
Flux for source dataset 1: 1.94551e-13 ergs/cm**2/s
Calculate the integrated background photon flux over the range 2 to 10 keV:
sherpa> BEFLUX (2.0:10.0)
Flux for background dataset 1: 3.59906e-13 ergs/cm**2/s
Calculate the energy flux at a single energy (2.0 keV) for the power-law
component of a source expression:
sherpa> SOURCE 1 = XSWABS[A] * POW[P]
sherpa> EFLUX 1 (2.0) P
Flux for source dataset 1: 1.73452e-14 ergs/cm**2/s/keV
Calculate the total energy flux over the energy range
2.0 to 4.0 keV for a model stack:
sherpa> FOO = POW[P] + GAUSS[G]
sherpa> SOURCE 1 = XSWABS[A] * FOO
sherpa> EFLUX 1 (2:4) FOO
Flux for source dataset 1: 2.46491e-13 ergs/cm**2/s
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