HEASARC Staff Scientist Position - Applications are now being accepted for a Staff Scientist with significant experience and interest in the technical aspects of astrophysics research, to work in the High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA Goddard Space Flight Center (GSFC) in Greenbelt, MD. Refer to the AAS Job register for full details.

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plcabs: powerlaw observed through dense, cold matter

This model describes X-ray transmission of an isotropic source of photons located at the center of a uniform, spherical distribution of matter, correctly taking into account Compton scattering. The model can be used for radial column densities up to $5\times 10^{-24}$ cm$^{-2}$. The valid energy range for which data can be modeled is between 10 and 18.5 keV, depending on the column density. Details of the physics of the model, the approximations used and further details on the regimes of validity can be found in Yaqoob (1997). In this particular incarnation, the initial spectrum is a power law modified by a high-energy exponential cut-off above a certain threshold energy.

Also, to improve the speed, a FAST option is available in which a full integration over the input spectrum is replaced by a simple mean energy shift for each bin. This option is obtained by setting par9 to a value of 1 or greater and cannot be made variable. Further, for single-scattering albedos less than the critical albedo (i.e. par8) energy shifts are neglected altogether. The recommended value for par8 is 0.1 which corresponds to about 4 keV for cosmic abundances and is more than adequate for ASCA data.

Note that for column densities in the range $10^{23}$ – $10^{24}$ cm$^{-2}$, the maximum number of scatterings which need be considered for convergence of the spectrum of better than 1% is between 1 and 5. For column densities as high as $5\times 10^{24}$ cm$^{-2}$, the maximum number of scatterings which need be considered for the same level of convergence is 12. This parameter cannot be made variable.

par1 Column density in units $10^{22}$ cm$^{-2}$
par2 Maximum number of scatterings to consider.
par3 Iron abundance.
par4 Iron K edge energy.
par5 Power-law photon index.
par6 High-energy cut-off threshold energy.
par7 High-energy cut-off e-folding energy.
par8 Critical albedo for switching to elastic scattering.
par9 If par9 >1, function uses mean energy shift, not integration.
par10 Source redshift, z
norm Normalization factor
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Next: polconst: Constant polarization Up: Additive Model Components Previous: pexriv: reflected powerlaw, ionized
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Last modified: Friday, 23-Aug-2024 13:20:40 EDT

HEASARC Staff Scientist Position - Applications are now being accepted for a Staff Scientist with significant experience and interest in the technical aspects of astrophysics research, to work in the High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA Goddard Space Flight Center (GSFC) in Greenbelt, MD. Refer to the AAS Job register for full details.