2017MNRAS.472.1361B

We explore spectral properties of a two-component advective flow around a neutron star. We compute the effects of thermal Comptonization of soft photons emitted from a Keplerian disc and the boundary layer of the neutron star by the post-shock region of a sub-Keplerian flow, formed due to the centrifugal barrier. The shock location X_s is also the inner edge of the Keplerian disc. We compute a series of realistic spectra assuming a set of electron temperatures of the post-shock region T_CE, the temperature of the Normal BOundary Layer (NBOL) T_NS of the neutron star and the shock location X_s. These parameters depend on the disc and halo accretion rates ({dot}m_d and {dot}m_h, respectively) that control the resultant spectra. We find that the spectrum becomes harder when {dot}m_h is increased. The spectrum is controlled strongly by T_NS due to its proximity to the Comptonizing cloud since photons emitted from the NBOL cool down the post-shock region very effectively. We also show the evidence of spectral hardening as the inclination angle of the disc is increased.