We investigate the behavior of the high frequency quasi-periodic oscillations ( QPOs ) in 4U 0614+091 , combining timing and spectral analysis of RXTE observations .
The energy spectra of the source can be described by a power law ( \alpha \sim 2.8 ) and a blackbody ( kT \sim 1.5 ) , with the blackbody accounting for 10–20 % of the total energy flux .
We find a robust correlation of the frequency , \nu , of the higher frequency QPO near 1 kHz with the flux of the blackbody , F _ { BB } .
The slope of this correlation , d \log { \nu } / d \log { F _ { BB } } , is 0.27 to 0.37 .
The source follows the same relation even in observations separated by several months .
The QPO frequency does not have a similarly unique correlation with the total flux or the flux of the power law component .
The RMS fraction of the higher frequency QPO rises with energy from 6.8 \pm 1.5 % ( 3–5 keV ) to 21.3 \pm 4.0 % ( 10–12 keV ) .
For the lower frequency QPO , however , it is consistent with a constant value of 5.4 \pm 0.9 % .
The results may be interpreted in terms of a beat frequency model for the production of the high frequency QPOs .