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We study the timing properties of the low mass X-ray binary 4U 1728-34 usingrecently released data from the Rossi X-Ray Timing Explorer. This binary, likemany others with accreting neutron stars, is known to exhibit strongquasi-periodic oscillations (QPOs) of its X-ray flux near 1 kHz. In addition tothe kilohertz QPOs, the Fourier power spectra show a broken power law noisecomponent, with a break frequency between 1 and 50 Hz, and a Lorentzian between10 and 50 Hz. We find that the frequencies of the break and the low-frequencyLorentzian are well correlated with the frequencies of the kilohertz QPOs. Theslope of the correlation is similar to that expected if the oscillations aredue to relativistic frame dragging (Lense-Thirring precession) in the inneraccretion disk (Stella & Vietri 1998). The correlation is also nearly identicalto the one found in Z-sources between the the well known QPOs on the horizontalbranch and the kilohertz QPOs, suggesting that the low frequency oscillationsare a similar phenomenon in these sources. The frequency of the break in thepower spectra is also correlated with the frequencies of the kilohertz QPOs. Aspreviously noted for the similar binaries 4U 1608-50 and 4U 1705-44, thisbroken power law component closely resembles that of black hole candidates inthe low state, where the break frequency is taken as an indicator of massaccretion rate. The relation between break frequency and kilohertz QPOfrequency thus provides additional proof that the frequency of the kilohertzQPOs increases with mass accretion rate.

Strong Correlation between Noise Features at Low Frequency and the KilohertzQuasi-Periodic Oscillations in the X-Ray Binary 4U 1728−34