Study on the correlations between the twin kilohertz quasi-periodic oscillations in low-mass X-ray binaries

The recently updated data of the twin kilohertz quasi-periodic oscillations (kHz QPOs) in the neutron star low-mass X-ray binaries are analyzed. The power-law fitting ν1 = a(ν2/1000)b and linear fitting ν2 = Aν1 + B are applied, individually, to the data points of four Z sources (GX 17+2, GX 340+0, GX 5−1 and Sco X−1) and four Atoll sources (4U 0614+09, 4U 1608−52, 4U 1636−53 and 4U 1728−34). The χ2-tests show that the power-law correlation and linear correlation both can fit data well. Moreover, the comparisons between the data and the theoretical models for kHz QPOs are discussed.