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tokens: f NS , One can see from these equations that the luminosity of seed photons produced by the NS surface anticorrelates with the NS spin. For higher spin sources, supply of the seed photons will be reduced resulting in stronger Comptonization, in particular in large Compton amplification factor A and Comptonization parameter y , in the same way as the dichotomy between BH and NS sources had been explained in Paper I . Furthermore, assuming that the emission from the boundary layer is well approximated by a blackbody spectrum, then L bl ∝ T 4 . This means that if all other factors (especially the emitting surface area) are similar across the population of NSs, the temperature of the seed photons . The maximal Keplerian frequency in the accretion disc is of the order of f K ∼ 1.6–1.8 kHz (Sibgatullin Sunyaev 2000 ), while NS spins vary in the f NS ∼ 0.3–0.6 kHz range. At L X / L Edd ∼ 0.05, the seed photon temperature varies in the kT BB ∼ 0.8–1.0 keV range, i.e. by a factor of about ∼1.2–1.3, between low- and high-spin sources (Fig. 3 ). In order to explain such a difference between f NS ∼ 0.3 kHz and f NS ∼ 0.6 kHz sources, α ∼ 0.7 is required, which is broadly consistent with the conclusions of Paper I that the accreting material reaches the surface of the NS still possessing about ∼1/3–1/2 of its initial energy. 5.1 Can fast spinning NSs mimic BHs? From equation ( 2 ), at sufficiently high NS spin frequencies the luminosity of the boundary layer can become small. Theoretically, this can make accreting NSs similar to BHs from the point of view of the energy balance in the Comptonization region. Indeed, such a behaviour is evident in Fig. 4 where the high-spin sources at high Eddington ratios progressively overlap with the region of Comptonization parameters, identified with BHs in Paper I . This dilutes the boundary between BHs and NSs. From Fig. 2 , one can see that three sources expand into y ≳1.0 regions at higher L / L Edd : 4U 1636–536, KS 1731–260 and, most significantly, GS 1826–238. This behaviour is strongest at the highest Eddington ratios (but still compatible with the source being in the hard spectral state). All these sources have high spin (>500 Hz), and their behaviour markedly contrasts with that of the slower sources at similar L / L Edd , such as 4U 1728–34, the Comptonizing strength of which remains low. For GS 1826–238, which has one of the highest spins and mass accretion rates in our sample, the Comptonization parameter can reach values y ∼ 1.25, which is inside the region occupied by BH LMXBs. 2 However, such high values of y are achieved only at high Eddington ratios, L X / L Edd ∼ 0.1, at which NSs are characterized by extremely low electron temperature, kT e ∼ 10–20 keV (Fig. 2 ), well below values typical for BHs (fig. 5 in Paper I ). This behaviour in kT e − y distinguishes NSs from BHs and is illustrated in Fig. 5 . A detailed comparison of high-spin NSs with BHs will be a subject of a separate study. As a final