|AHELP for CIAO 4.9 Sherpa v1||
Simple reflection model good up to 15 keV. XSPEC model.
A simple multiplicative reflection model due to Tahir Yaqoob.
This is a multiplicative model component.
|1||thetamin||minimum angle (degrees) between source photons incident on the slab and the slab normal (=arctan(Ri/H)|
|2||thetamax||maximum angle (degrees) between source photons incident on the slab and the slab normal (=arctan(Ro/H).|
|3||thetaobs||angle (degrees) between the observer's line of sight and the slab normal.|
|4||feabun||iron abundance relative to Solar|
|5||fekedge||iron K-edge energy|
|6||escfrac||fraction of the direct flux seen by the observer|
|7||covfac||normalization of the reflected continuum|
This model gives the reflected X-ray spectrum from a cold, optically thick, circular slab with inner and outer radii Ri and Ro respectively, illuminated by a point source a height H above the centre of the slab. The main difference between this and other reflection models is that analytic approximations are used for the Chandrasekar H functions (and their integrals) and ELASTIC SCATTERING is assumed (see Basko 1978, ApJ, 223, 268). The elastic scattering approximation means that the model is ONLY VALID UP TO ~ 15 keV in the source frame. Future enhancements will include fudge factors which will allow extension up to 100 keV. The fact that no integration is involved at any point makes the routine very fast and particularly suitable for generating error contours, especially when fitting a large number of data channels.The model is multiplicative so can be used with ANY incident continuum.
Suppose the incident photon spectrum is N(E) photons/cm/cm/s/keV and that the incident continuum is steady in time and further that the reflected continuum from the slab is R(E). When you multiply the incident spectrum with HREFL, what you actually get is
M(E) = escfrac * N(E) + covfac * R(E)
Thus, the actual physical situation described above corresponds to Escfrac=1.0 and covfac=1.0. You may decide to float Escfrac and/or covfac. In that case, you must decide for your particular case what the best-fitting values of these parameters mean physically. It may imply time-lags between the direct and reflected components, different source and/or disk geometries to those assumed or something else.
This information is taken from the XSPEC User's Guide. Version 12.9.0o of the XSPEC models is supplied with CIAO 4.9.
For a list of known bugs and issues with the XSPEC models, please visit the XSPEC bugs page.
To check the X-Spec version used by Sherpa, use the get_xsversion routine from the xspec module:
sherpa> from sherpa.astro.xspec import get_xsversion sherpa> get_xsversion() '12.9.0o'
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