Optxagnf, optxagn: Colour temperature corrected disc and energetically coupled Comptonisation model for AGN.

AGN spectral energy distributions are complex, but can be phenomenologically fit by a disc, optically thick, low temperature thermal Comptonisation (to produce the soft X-ray excess) and an optically thin, high temperature themal Comptonisation (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 (colour 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, $\dot{M}$, 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 $L_{tot} = eff \dot{M} c^2$, where the efficiency is set by black hole spin assuming Novikov-Thorne emissivity.

There are two versions of the model. optxagnf is the one recommended for most purposes, and has the colour temperature correction calculated for each temperature from the approximations given in Done et al. (2012). optxagn instead allows the user to define their own colour temperature correction, $f_{col}$, 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 normalisations MUST be frozen at unity.

Parameters in optxagnf:

par1	mass, black hole mass in solar masses
par2	dist, comoving (proper) distance in Mpc
par3	$\log L/L_{edd}$, Eddington ratio
par4	$a_{star}$, dimensionless black hole spin
par5	$r_{cor}$, coronal radius in $R_g = GM/c^2$ marking the transition from (colour temperature corrected) blackbody emission to a Comptonised spectrum. If this parameter is negative then only the blackbody component is used.
par6	$\log r_{out}$, 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)
par7	$kT_e$, electron temperature for the soft Comptonisation component (soft excess) in keV
par8	$\tau$, pptical depth of the soft Comptonisation component. If this parameter is negative then only the soft Compton component is used.
par9	$\Gamma$, spectral index of the hard Comptonisation component (“power law”) which has temperature fixed to 100 keV.
par10	$f_{pl}$, fraction of the power below $r_{cor}$ which is emitted in the hard comptonisation component. If this parameter is negative then only the hard Compton component is used.
par11	Redshift
norm	K, must be frozen

Parameters in optxagn:

par1	mass, black hole mass in solar masses
par2	dist, comoving (proper) distance in Mpc
par3	$\log L/L_{edd}$, Eddington ratio
par4	$a_{star}$, dimensionless black hole spin
par5	$r_{cor}$, coronal radius in $R_g = GM/c^2$ marking the transition from (colour temperature corrected) blackbody emission to a Comptonised spectrum. If this parameter is negative then only the blackbody component is used.
par6	$\log r_{out}$, 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)
par7	$kT_e$, electron temperature for the soft Comptonisation component (soft excess) in keV
par8	$\tau$, pptical depth of the soft Comptonisation component. If this parameter is negative then only the soft Compton component is used.
par9	$\Gamma$, spectral index of the hard Comptonisation component (“power law”) which has temperature fixed to 100 keV.
par10	$f_{pl}$, fraction of the power below $r_{cor}$ which is emitted in the hard comptonisation component. If this parameter is negative then only the hard Compton component is used.
par11	$f_{col}$, colour temperature correction to apply to the disc blackbody emission for radii below $r_{cor}$ with effective temperature $>~T_{scatt}$
par12	$T_{scatt}$, effective temperature criterion used as described above (in K).
par13	Redshift
norm	K, must be frozen

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Last modified: Wednesday, 12-Mar-2025 17:05:24 EDT