|AHELP for CIAO 4.9 Sherpa v1||
Color-temperature-corrected disc and energetically coupled Comptonization model for AGN. XSPEC model.
AGN spectral energy distributions are complex, but can be phenomenologically fit by a disc, optically thick, low temperature thermal Comptonization (to produce the soft X-ray excess) and an optically thin, high temperature themal Comptonization (to produce the power law emission which dominates above 2 keV). Here we combine these three components together assuming that they are all ultimately powered by gravitational energy released in accretion. We assume that the gravitational energy released in the disc at each radius is emitted as a (color-temperature-corrected) blackbody only down to a given radius, R_corona. Below this radius, we further assume that the energy can no longer completely thermalise, and is distributed between powering the soft excess component and the high energy tail. This imposes an important energetic self consistency on the model. The key aspect of this model is that the optical luminosity constrains the mass accretion rate through the outer disc, M_dot, provided there is an independent estimate of the black hole mass (from, e.g., the H-beta emission line profile). The total luminosity available to power the entire SED is [L_tot=eff M_dot c^2], where the efficiency is set by black hole spin assuming Novikov-Thorne emissivity.
There are two versions of the model: xsoptxagnf is the one recommended for most purposes, and has the color-temperature correction calculated for each temperature from the approximations given in Done et al. (2012); xsoptxagn instead allows the user to define their own color-temperature correction, fcol, which is then applied to annuli with effective temperature > T_scatt. In both models the flux is set by the physical parameters of mass, L/L_Edd, spin and distance, hence the model normalizations MUST be frozen at unity.
This is an additive model component.
|1||mass||Black hole mass in solar masses|
|2||dist||Luminosity distance in Mpc|
|4||astar||Dimensionless black hole spin|
|5||rcor||Coronal radius in R_g=GM/c^2 marking the transition from (color temperature corrected) blackbody emission to a Comptonised spectrum. If this parameter is negative then only the blackbody component is used.|
|6||logrout||Log of the outer radius of the disc in units of R_g; if this is '-ve' the code will use the self gravity radius as calculated from Laor & Netzer (1989)|
|7||kT_E||Electron temperature for the soft Comptonization component (soft excess) in keV|
|8||tau||Optical depth of the soft Comptonization component. If this parameter is negative then only the soft Compton component is used.|
|9||Gamma||Spectral index of the hard Comptonization component ('power law') which has temperature fixed to 100 keV. If this parameter is negative then only the hard Compton component is used.|
|10||fpl||Fraction of the power below rcor which is emitted in the hard Comptonization component|
|11||fcol||Color-temperature correction to apply to the disc blackbody emission for radii below rcor with effective temperature > Tscatt|
|12||tscat||Effective temperature criterion used as described above.|
|14||norm||Normalization, must be frozen|
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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