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sssed: Shakura & Sunyaev spectral energy distribution

The SSsed model was developed by Kubota et al. (2024 MNRAS 528, 1668) to describe spectral energy distribution (SED) of black hole binaries (BHBs). This model is a revised version of the agnsed model (Kubota & Done 2018, MNRAS, 489, 524), but it was tuned to BHBs, and especially to their intermediate spectra where there are clearly two Compton components as well as (truncated) disc. The key concept is that the flow is radially stratified such that the accretion power is emitted as (colour-corrected) black body radiation at $r > r_{cor}$, while it is emitted as inverse-Comptonization by both the thermal and non-thermal corona at $r < r_{cor}$. The seed photons are assumed to be emitted from the underlying passive disc at $r < r_{cor}$. All the emission is constrained by the standard disc emissivity by Shakura & Sunyaev (1973), with $Mdot$ constant with radius. If the components of the outer disc are visible, both parameters $r_{cor}$ and $r_{in}$ are determined independently. In cases where the outer disc is not visible, such as in the bright hard state, caution is needed in interpreting the obtained value of $r_{cor}$.

The parameters of the SSsed model are summarised below. Note that the model has some switching parameters controlling the following behaviors::

  • If parameter 6 is negative, the model gives the inner hot Comptonisation component.
  • If parameter 7 is negative, the model gives the Comptonisation component in the passive-disc corona region.
  • If parameter 9 is negative, the model gives the outer disc.
  • If parameter 12 is -1, the code will use the self-gravity radius as calculate from Laor & Netzer (1989, MNRAS, 238, 897).
  • Colour correction is included when parameter 14 is set to 1, while it is not included when this parameter is set to 0. For BHB spectra, this parameter should be fixed at 1.

par1 mass, black hole mass in solar masses
par2 dist, comoving (proper) distance in kpc
par3 logmdot, $log(mdot)$ where $mdot = Mdot/Mdot_{Edd}$ and where $Mdot_{Edd}c^2 = L_{Edd}$
par4 Rin, $r_in$ inner most radius of the accretion flow in $r_g$
par5 cosi, $cos(i)$ inclination angle of the disc
par6 kTe_th, $kT_{e,th}$ electron temperature for thermal corona in keV. If this parameter is negative, the model gives the inner hot Comptonisation component.
par7 kTe_nt, $kT_{e,nth}$ apparent electron temperature for non-thermal corona in keV which is recommended to be fixed at 300 keV to mimic non-thermal electron distribution. If this parameter is negative, the model gives the Comptonisation component in the passive-disc corona region.
par8 Gamma_th, $\Gamma_{th}$ photon index of inner hot corona. If this parameter is negative, then only the inner Compton component is used.
par9 Gamma_nt, $\Gamma_{nth}$ photon index of disc-corona. If this parameter is negative, the model gives the outer disc.
par10 frac_th, $f_{th}$ fraction of the hot Comptonising component to the total Comptonisation
par11 Rcor, $r_{cor}$ outer radius of the disc-corona region in $r_g$
par12 logrout, outer radius of accretion disc in . If this parameter is -1, the code will use the self gravity radius as calculated from Laor & Netzer (1989)
par13 redshift must be fixed
par14 color_cor, switching parameter for colour correction (0: no colour correction, 1: colour correction factor is calculated by the same way as optxagnf (Done et al. 2012 MNRAS, 420, 1848)
norm must be fixed at 1
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Next: step: step function convolved Up: Additive Model Components Previous: ssa: Strangeon star atmosphere   Contents