Paolo Coppi's hybrid (thermal/non-thermal) hot plasma emission model

NOTE: This model is now in the Xspec release and this page is superceded by the Xspec manual

These three models are based on Paolo Coppi's hybrid thermal/non-thermal hot plasma emission model for X-ray binaries. The underlying physics and a detailed description of the code are included in this draft paper. Do not use these models without reading and understanding this paper. The original website for these models is The parameters for eqpair are

par1 = l_h/l_s, ratio of the hard to soft compactnesses
par2 = l_bb, the soft photon compactness
par3 = kT_bb, if > 0 then temperature of the inner edge of the accretion disk for the diskbb model; if < 0 then abs(kT_bb) is the T_max parameter for the diskpn model.
par4 = l_nt/l_h, fraction of power supplied to energetic particles which goes into accelerating non-thermal particles.
par5 = tau_p, the Thomson scattering depth.
par6 = radius, the size of the scattering region (cm).
par7 = g_min, minimum Lorentz factor of the pairs.
par8 = g_max, maximum Lorentz factor of the pairs.
par9 = G_inj, if < 0 then non-thermal spectrum is assumed mono-energetic at g_max; if > 0 then a power-law from g_min to g_max.
par10 = pairinj, if = 0 then accelerated particles are electrons from thermal pool; if = 1 then accelerated particles are electrons and positrons.
par11 = cosIncl, inclination of reflecting material wrt line-of-sight.
par12 = Refl, fraction of scattering region's emission intercepted by reflecting material.
par13 = Fe_abund, relative abundance of iron.
par14 = Ab>He, relative abundance of other metals.
par15 = T_disk, temperature of reflecting disk.
par16 = xi, ionization parameter of reflector.
par17 = Beta, power-law index with radius of disk reflection emissivity.
par18 = Rin, inner radius of reflecting material (GM/c^2).
par19 = Rout, outer radius of reflecting material (GM/c^2).
par20 = redshift.

Simplified models eqtherm and compth are provided for cases where non-thermal processes are not important and photon-photon pair production can be ignored. These should only be used if l_bb <~ 10.

The source code and required data files are included in this gzipped tar file. You will need to edit the file xseqpair.f to ensure that DATADIR points to the correct directory.

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

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Last modified: Tuesday, 14-Feb-2023 16:42:00 EST