Thermal and bulk Comptonization for cylindrical accretion onto the polar cap of a magnetized neutron star

This model describes the spectral formation in the accretion column onto the polar cap of a magnetized neutron star. Both thermal and bulk Comptonization processes are taken into account. The details for the method adopted for the numerical solution of the radiative transfer equation are reported in Farinelli et al. (2012, A&A, 538, A67). This model can be used for spectral fitting of both accreting X-ray pulsars and Supergiant Fast X-ray Trasients.

The model parameters are the following:

par1  =  kTbb, temperature of the seed blackbody spectrum (keV)

par2  =  kTe, electron temperature of the accretion colum (keV)

par3  =  τ, vertical optical depth of the accretion column, with electron cross-section equal to 10-3 of the Thomson cross-section

par4  =  η, index of the velocity profile when the accretion velocity increases towards the neutron star (valid when par8=1)

par5  =  β0, terminal velocity of the accreting matter at the neutron star surface (valid when par8=1)

par6  =  r0, radius of the accretion column in units of the neutron star Schwarzschild radius

par7  =  A, albedo at the neutron star surface

par8 =  Flag for setting the velocity profile of the accretion column
                    if =  1  β(z)=A (Zs/Z), where A=β0 (Z0/Zs)η
                    if =  2  β(τ)=-α τ

par9 =  Cn, normalization constant defined as  R2km /D210, where  Rkm and D10 are the accretion column radius in km and the source distance
                    in units of 10 kpc, respectively

The  contains the source code, the model parameter file and a brief PDF cookbook with instructions for installing compmag as an XSPEC local model.