flux
calculate fluxes
Calculate the flux of the current model between certain limits.
Syntax: flux [<lowEnergy>[<hiEnergy>]] [err
<number><level>|noerr]
where <lowEnergy> and <hiEnergy> are the values over which
the flux is calculated. Initial default values are 2 to 10 keV.
The flux is given in units of photons
and ergs
.
The energy range must be contained by the range covered by the current spectra
(which determine the range over which the model is evaluated). Values outside
this range will be reset automatically to the extremes. Note that the energy
values are two separate arguments, and are NOT connected by a dash. (see
parameter ranges in the freeze command).
The flux will be calculated for all loaded spectra. If no spectra are loaded
(or none of the loaded spectra have a response), the model is evaluated over
the energy range determined by its dummy response. (In XSPEC12, models are
automatically assigned default dummy responses when there is no data, so the
dummyrsp command need not be given.) If more than 1 model has been loaded,
whichever model the user has specified to be the active one for a given
source is the one used for the flux calculation.
The results of a flux command may be retrieved by the tclout flux
<n> command where n is the particular spectrum of interest. If the
flux was calculated for the case of no loaded spectra, the results can be
retrieved by tclout flux with the <n> argument omitted.
The err/noerr switch sets whether errors will be estimated on the
flux. The error algorithm is to draw parameter values from the distribution
and calculate a flux. <number> of sets of parameter values will be
drawn. The resulting fluxes are ordered and the central <level>
percent selected to give the error range. You can get the full array of
simulated flux values by calling tclout flux with the errsims
option (see tclout command).
When Monte Carlo Markov Chains are loaded (see chain command), they
will provide the distribution of parameter values for the error estimate.
Otherwise the parameter values distribution is assumed to be a
multivariate Gaussian centered on the best-fit parameters with sigmas
from the covariance matrix. This is only an approximation in the case that
fit statistic space is not quadratic.
There is also a model component cflux which can be used to
estimate fluxes and errors for part of the model. For instance, defining
the model as wabs(pow + cflux(ga)) provides a fit parameter which gives
the flux in the gaussian line.
Examples:
The current data have significant responses to data within 1.5 to 18 keV.
XSPEC12> flux
//Calculate the current model flux over the default range.
XSPEC12> flux 6.4 7.0
//Calculate the current flux over 6.4 to 7 keV
XSPEC12> flux 1 10
//The flux is calculated from 1.5 keV (the lower limit of the
//current response's sensitivity) to 10 keV.
HEASARC Home |
Observatories |
Archive |
Calibration |
Software |
Tools |
Students/Teachers/Public
Last modified: Friday, 23-Aug-2024 13:20:40 EDT
|