tbabs, ztbabs, tbfeo, tbgas, tbgrain, tbpcf, tbvarabs, tbrel: ISM grain absorption

The Tuebingen-Boulder ISM absorption model. This model calculates the cross section for X-ray absorption by the ISM as the sum of the cross sections for X-ray absorption due to the gas-phase ISM, the grain-phase ISM, and the molecules in the ISM. In the grain-phase ISM, the effect of shielding by the grains is accounted for, but is extremely small. In the molecular contribution to the ISM cross section, only molecular hydrogen is considered. In the gas-phase ISM, the cross section is the sum of the photoionization cross sections of the different elements, weighted by abundance and taking into account depletion onto grains.

In addition to the updates to the photoionization cross sections, the gas-phase cross section differs from previous values as a result of updates to the ISM abundances. These updated abundances are available through the abund wilm command. Details of updates to the photoionization cross sections as well as to abundances can be found in Wilms, Allen & McCray (2000).

Two versions of this model are available depending on the setting of TBABSVERSION. The newer version (the default) dates from 2016 and includes high resolution edge structures for the K-edges of oxygen and neon and the L-edges of iron. The newer version is 25 times faster than the older version or the phabs model. To recover the older version use xset TBABSVERSION 1.

The parameters which reference abundances relative to Solar are using the Solar abundances as set by the abund command.

tbabs allows the user to vary just the hydrogen column.

par1=$nH$

equivalent hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)

ztbabs is similar, but allows the user to set a fixed redshift parameter

par1=$nH$	equivalent hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)
par2=$z$	redshift

tbfeo is similar, but allows the user to vary the oxygen and iron abundances

par1=$nH$	equivalent hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)
par2=$O$	oxygen abundance relative to Solar
par3=$Fe$	iron abundance relative to Solar
par4=$z$	redshift

tbgas is similar to ztbabs but with no grain absorption

par1=$nH$	equivalent hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)
par2=$z$	redshift

tbgrain allows the user to vary the molecular hydrogen column and the grain distribution parameters.

par1	equivalent hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)
par2	fraction of hydrogen existing in molecular form as H2
par3	grain density (in gm cm$^{-3}$)
par4	grain minimum size (in $\mu$m)
par5	grain maximum size (in $\mu$m)
par6	power-law index of grain sizes

tbpcf is similar to ztbabs but a partial covering fraction parameter

par1=$nH$	equivalent hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)
par2=$pcf$	partial covering fraction
par3=$z$	redshift

tbvarabs additionally allows the user to vary the elemental abundances and the redshift

par1	equivalent hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)
par2 -par18	abundance (relative to Solar) of He, C, N, O, Ne, Na, Mg, Al, Si, S, Cl, Ar, Ca, Cr, Fe, Co, Ni
par19	molecular hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)
par20	grain density (in gm cm$^{-3}$)
par21	grain minimum size (in $\mu$m)
par22	grain maximum size (in $\mu$m)
par23	power-law index of grain sizes
par24-par41	grain depletion fractions of He, C, N, O, Ne, Na, Mg, Al, Si, S, Cl, Ar, Ca, Cr, Fe, Co, Ni
par42	redshift

tbrel is similar to tbvarabs but the interpretation of the abundances is different in that this model also allows “negative” nH. Use this, e.g., if you want to measure changes in column relative to an average column. For example, you can fit a model such as tbrel*tbabs*continuum, where all values of tbabs are frozen at the average column of the source. If the fit results in a negative column for nH during that observation, then the total column of the source is less than the average.

par1	equivalent hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)
par2 -par18	abundance (relative to Solar) of He, C, N, O, Ne, Na, Mg, Al, Si, S, Cl, Ar, Ca, Cr, Fe, Co, Ni
par19	molecular hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)
par20	grain density (in gm cm$^{-3}$)
par21	grain minimum size (in $\mu$m)
par22	grain maximum size (in $\mu$m)
par23	power-law index of grain sizes
par24-par41	grain depletion fractions of He, C, N, O, Ne, Na, Mg, Al, Si, S, Cl, Ar, Ca, Cr, Fe, Co, Ni
par42	redshift

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