6 High-Frequency Variability in Neutron-Star Low-Mass X-ray Binaries
303
Fig. 6.25 Quality factor of the lower (filled symbols) and the upper (open symbols) kHz QPOs as a
function of the QPO frequency for seven atoll sources, 4U 1608−52, 4U 1636−53, 4U 1728−34,
Aql X-1, 4U 1820−30, 4U 1735−44, and 4U 0614+09, and five Z sources, Sco X-1, Cyg X-2,
GX 17+2, GX 5-1, and GX 340+0 [103]. Notice that, as with the fractional rms (Fig. 6.21), the
scale of the y axis is different for atoll and Z sources, reflecting the fact that the maximum value
of the quality factor is larger in the former than in the latter
303
Fig. 6.25 Quality factor of the lower (filled symbols) and the upper (open symbols) kHz QPOs as a
function of the QPO frequency for seven atoll sources, 4U 1608−52, 4U 1636−53, 4U 1728−34,
Aql X-1, 4U 1820−30, 4U 1735−44, and 4U 0614+09, and five Z sources, Sco X-1, Cyg X-2,
GX 17+2, GX 5-1, and GX 340+0 [103]. Notice that, as with the fractional rms (Fig. 6.21), the
scale of the y axis is different for atoll and Z sources, reflecting the fact that the maximum value
of the quality factor is larger in the former than in the latter