An ionized absorber based on that of Done et al. (1992, ApJ 395, 275) and developed by Magdziarz & Zdziarski. See also Zdziarski et al. (1995, ApJ 438, L63). Photoionization rates are from Reilman & Manson (1979, ApJS 40, 815), who employ the Hartree-Slater approximation (accurate to about 5%), and recombination rates are from Shull & Steenburg (1982, ApJS 48, 95). The cross sections are extrapolated with E-3 above 5 keV. The abundances are set up by the command abund. Send questions or comments to firstname.lastname@example.org.
|par1||=||power-law photon index.|
|par2||=||Hydrogen column in units of 1022 cm-2.|
|par3||=||Absorber temperature in K.|
|par4||=||Absorber ionization state (L/nR2), see Done et al. (1992).|
|par6||=||Iron abundance relative to that defined by the command abund.|
This model accounts for the decay in the ACIS quantum efficiency most likely caused by molecular contamination of the ACIS filters. The user needs to supply the number of days between Chandra launch and observation. The acisabs parameters related to the composition of the hydrocarbon and the rate of decay should be frozen and not modified. The present version of acisabs is to be used for the analysis of bare ACIS I and ACIS S data. For the present version of acisabs one must use the standard qe file vN0003 instead of the optional vN0004 file.
Because of the present large uncertainity in the ACIS gain at energies below 350eV we recommend that events in the 0-350eV range be ignored in the spectral analysis until the gain issue is resolved.
acisabs calculates the mass absorption coefficients of the contaminant from atomic scattering factor files provided at http://www-cxro.lbl.gov/optical_constants/asf.html
|par1||=||Days between Chandra launch and ACIS observation|
|par2||=||Slope of linear quantum efficiency decay|
|par3||=||Offset of linear quantum efficiency decay|
|par4||=||Number of carbon atoms in hydrocarbon|
|par5||=||Number of hydrogen atoms in hydrocarbon|
|par6||=||Number of oxygen atoms in hydrocarbon|
|par7||=||Number of nitrogen atoms in hydrocarbon|
Non-relativistic, optically-thin Compton scattering.
where is the Thomson cross-section.
|par1||=||hydrogen column (in units of 1022 atoms/cm2)|
|par1||=||depth of the fundamental|
|par3||=||width of the fundamental|
|par4||=||depth 2nd harmonic|
|par5||=||width of the 2nd harmonic|
|par1||=||scattering fraction at 1 keV|
|par2||=||size of halo at 1 keV in units of the detector beamsize|
|par2||=||absorption depth at the threshold|
An exponential table model. The filename to be used should be given immediately after etable in the model command. For example
uses mymod.mod as the input for the model. XSPEC will multiply the contents of the model by -1 then take the exponential ie this model is for calculating absorption functions. For specifications of the table model file, see the OGIP memo 92-009 on the FITS file format for table model files (available on the WWW or by anonymous ftp from ftp://legacy.gsfc.nasa.gov/caldb/docs/memos).
|par1||=||e-folding energy for the absorption|
|par1||=||amplitude of effect|
|par3||=||start energy of modification|
|par1||=||cutoff energy in keV|
|par2||=||e-folding energy in keV|
|par1||=||minimum angle (degrees) between source photons incident on the slab and the slab normal (=arctan(Ri/H).|
|par2||=||maximum angle (degrees) between source photons incident on the slab and the slab normal (=arctan(Ro/H).|
|par3||=||Angle (degrees) between the observer's line of sight and the slab normal.|
|par4||=||Iron abundance relative to Solar.|
|par5||=||Iron K-edge energy.|
|par6||=||Fraction of the direct flux seen by the observer.|
|par7||=||Normalization of the reflected continuum.|
Thus, the actual physical situation described above corresponds to par6=1.0 and par7=1.0. You may decide to float par6 and/or par7. In that case, you must decide what the best-fitting values of these parameters mean physically for your case. It may imply time-lags between the direct and reflected components, different source and/or disk geometries to those assumed, or something else.
uses mymod.mod as the input for the model. For specifications of the table model file, see the OGIP memo 92-009 on the FITS file format for table model files (available on the WWW or by anonymous ftp from ftp://legacy.gsfc.nasa.gov/caldb/docs/memos). An example multiplicative table model file is testpcfabs.mod in $XANADU/src/spectral/session.