Thermal and
bulk Comptonization for cylindrical accretion onto the polar cap of a
magnetized neutron star
NOTE: This model is now in the Xspec release and this page is superceded by the Xspec manual
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)-η,
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 tar file contains the source code, the model parameter
file and
a brief PDF cookbook with instructions for installing compmag as an
XSPEC local model.