Convolution Model Components

  
gsmooth

Gaussian smoothing with a variable sigma, which varies as the ${\tt par2}$power of the energy. The sigma at 6 keV is set with ${\tt par1}$.

$$\begin{array}{lcl} dC(E) & = & (1./(\sqrt{2\pi \sigma(E)^2}))... ...igma(E) & = & {\tt par1} (E/6 keV)^{{\tt par2}} \\ \end{array}$$

where :

par1			=		gaussian sigma at 6 keV
par2			=		power of energy for sigma variation

  
lsmooth

Lorentzian smoothing with a variable width, which varies as the par2 power of the energy. The width at 6 keV is set with par1.

$$\begin{array}{lcl} dC(E) & = & (\sigma(E)/2\pi) / ((E-X)^2 + ... ...igma(E) & = & {\tt par1} (E/6 keV)^{{\tt par2}} \\ \end{array}$$

where :

par1			=		lorentzian width at 6 keV
par2			=		power of energy for sigma variation

  
reflect

Convolution model for reflection from neutral material according to the method of Magdziarz & Zdziarski (1995, MNRAS, 273, 837). This is a generalization of the pexrav and bexrav models. When using this model it is essential to extend the energy range over which the model is calculated because photons at higher energies are Compton downscattered into the target energy range. The energy range can be extended using the extend command. The upper limit on the energies should be set above that for which the input spectrum has significant flux. See the help on pexrav or bexrav for further information and admonitions.

par1			=		reflection scaling factor (1 for isotropic source above disk)
par2			=		redshift, z
par3			=		abundance of elements heavier than He relative to the solar abundances
par4			=		iron abundance relative to the above
par5			=		$\cos i,$ the inclination angle

  
rgsxsrc

Convolution model for the analysis of moderately-extended ($\sim 1$ arcmin) sources, developed by Andy Rasmussen of the Columbia University XMM-Newton RGS instrument team. The code convolves the spectral model with an angular structure function for a given extended source. The structure function is taken directly from an image (e.g., XMM-Newton EPIC, Chandra ACIS etc) where the user provides RA and Dec (2000) coordinates for the source, position angle of the spacecraft, and an aperture size suitable for the source in order to characterize the convolution function. The model resulting from the convolution is then used with the standard RGS point source spectral response to fit data.

The user is required to have used the XSPEC command xset prior to defining the spectral model, e.g.:

XSPEC>xset rgs_xsource_file <filename>



This command points XSPEC to an external file containing the attitude and aperture information. A typical file must look like this :

RGS_XSOURCE_IMAGE

<filename of image of source>

RGS_XSOURCE_BORESIGHT

<image boresight in format>

RGS_XSOURCE_EXTRACTION

<size of region in arcminutes>

For example :

RGS_XSOURCE_IMAGE

</local/data/mymachine/myusername/MOS1.FIT>

RGS_XSOURCE_BORESIGHT

<05:25:02.9 -69:38:30 339.760974>

RGS_XSOURCE_EXTRACTION

<1.8>

The RA and Dec of the center of the source can be taken determined by the user from the image or taken from the headers of the source spectrum. The position angle can be found in the image headers.

The file is reread on each iteration so editing the file during an XSPEC session will cause these parameters to be changed. The only model parameter is

par1

=

the order of the spectrum (this number is always negative).

NB. The interpretation of results using this model is not trivial. The method assumes that the spatial distributions of the continuum and all lines are identical to the broad band image. This is unlikely to be the case. Resulting line velocities and profiles should be treated with appropriate caution.

Contact the US XMM_Newton GOF for help. xmmhelp@athena.gsfc.nasa.gov