Model related Keywords

 

 

The parameter string of the keyword MODEL has a more complex structure. It defines a spectral model, which contains additive and multiplicative parts. The additive parts represent the true kernel of the model, whereas the multiplicative parts have a filter function   (only dimensionless factors) like galactic or source intrinsic absorption.     The model   names are restricted to four characters, followed by a parenthesized parameter list containing the indices of the corresponding model parameters.   Different model parts can be separated by parenthesis, parameter lists of different model components may be overlapping:

MODEL mul1(1)*(add1(2,3)+mul2(4)*add2(5,6,7)+...)

The following example represents the standard model of a power law spectrum:

MODEL      gamm(1)*powl(2,3,4) ! gal_abs*power_law

    A second line can be used by closing the first line with an &:

MODEL      gamm(1)*(powl(2,3,4) + bbdy(5,6) &
           + thbr(7,8,9,10))

            The keyword PARAMETER has a list of parameters,   the meaning of which depends of one of its entries: mode. Its general structure has the following form:

PARAMETER sn [mode]

Values without brackets are mandatory, in square brackets [ ] are optional. The sequence number sn must correspond to the number given as an argument in a model part. The meaning of the model parameters depends of their mode value, which can be fixed (default), free interesting, uninteresting, prefit, or grid. In the default mode the parameter sn is fixed to its value . The mode free and uninteresting allows to fit the parameter sn. The only difference between free and uninteresting exists for the error calculation of the parameter, which will be not performed in the case of uninteresting.          

If four parameter values to are defined represents the starting value, the lower, the upper hard boundary, and the soft boundary, which is always taken relative to the actual parameter values. In the prefit mode only parameters with this mode are considered as free. In the automatic following main fit all parameters with a mode of either free interesting, uninteresting, or prefit are assumed as fitting parameters. Last but not least the grid mode allows to create a grid of one or two parameters by fitting the remaining parameters. The values of the parameter list correspond in this case to: = start, = end, and = step value. The maximum step number for each parameter is 50.

PARAMETER 1  0.1  .001  100.  0. free ! nH in 10^21 H-atoms/cm^2
PARAMETER 2  1.0  1.E-5 1.E+5 0. free ! flux amplitude at E0
PARAMETER 3  -1.5 -4.0 0.0    0. free ! photon index gamma
PARAMETER 4  1.0                      ! reference energy E0/keV

The following keywords are only relevant if a spectrum of a red shifted source is considered. Keyword REDSHIFT defines the cosmological red shift   . Its default value is zero. The luminosity distance will be calculated for a Friedmann-Lemaitre cosmology using the keywords HUBBLE_PARAMETER and DECELERATION_PARAMETER, which have default values = 50 km/s/Mpc and = 0.5, respectively.

REDSHIFT           1.5      ! red shift z
HUBBLE_PARAMETER   50.      ! Hubble parameter H0 in km/s/Mpc
DECELERATION_PAR   0.5      ! deceleration parameter q0

The sequence of keywords -- MODEL, PARAMETER, REDSHIFT, HUBBLE_PAR, and DECELERATION_PAR -- has to be in order and must appear always after the general keywords, which can be in any order. There is a possibility to analyze more than one model simply by adding other models.