Irradiation of the inner and outer disc

The inner disc can be irradiated by the Compton tail. This can substantially change the inner disc temperature structure from that expected from an unilluminated disc in the limit where the ratio of luminosity in the tail to that in the disc, Lc/Ld>>1. This is generally the case in the low/hard state of accreting black holes, and neglecting this effect leads to an underestimate of the inner disc radius (Gierlinski, Done & Page 2008a MNRAS, 388, 753).

The irradiated inner disc and Compton tail can illuminate the rest of the disc, and a fraction f_out of the bolometric flux is thermalised to thelocal blackbody temperature at each radius. This reprocessed flux generally dominates the optical and UV bandpass of LMXBs (Gierlinski, Done & Page 2008b MNRAS, submitted).

This model is built on top of the nthcomp model which must also be installed.

The model parameters are :

par1     =  kT_disk, innermost temperature of the UNILLUMINATED disc
par2     =  Gamma, asymptotic power-law photon index
par3     =  kT_e, electon temperature (high energy rollover)
par4     =  Lc/Ld, ratio of luminosity in the Compton tail to that of the UNILLUMINATED disc
par5     =  fin, fraction of luminosity in the Compton tail which is thermalised in the inner disc (this should generally be fixed at 0.1 as appropriate for an albedo of 0.3 and solid angle of 0.3)
par6     =  rirr, radius of the Compton illuminated disc in terms of the inner disc radius
par7     =  fout, fraction of bolometric flux which is thermalised in the outer disc
par8     =  logrout, log10 of the outer disc radius in terms of the inner disc radius
K     =  normalization, as in diskbb

The source code and model.dat entries are available.


Keith Arnaud, Lab. for High Energy Astrophysics, NASA/Goddard Space Flight Center

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Last modified: Thursday, 28-Aug-2008 15:15:52 EDT