Relations between Timing Features and Colors in the X‐Ray Binary 4U 0614+09

We study the correlations between timing and X-ray spectral properties in thelow mass X-ray binary 4U 0614+09 using a large (265-ks) data set obtained withthe Rossi X-ray Timing Explorer. We find strong quasi-periodic oscillations(QPOs) of the X-ray flux, like the kilohertz QPOs in many other X-ray binarieswith accreting neutron stars, with frequencies ranging from 1329 Hz down to 418Hz and, perhaps, as low as 153 Hz. We report the highest frequency QPO yet fromany low mass X-ray binary at 1329+-4 Hz, which has implications for neutronstar structure. This QPO has a 3.5-sigma single-trial significance, for anestimated 40 trials the significance is 2.4-sigma. Besides the kilohertz QPOs,the Fourier power spectra show four additional components: high frequency noise(HFN), described by a broken power-law with a break frequency between 0.7 and45 Hz, very low frequency noise (VLFN), which is fitted as a power-law below 1Hz, and two broad Lorentzians with centroid frequencies varying from 6 to 38 Hzand 97 to 158 Hz, respectively. We find strong correlations between thefrequencies of the kilohertz QPOs, the frequency of the 6 to 38 Hz broadLorentzian, the break frequency of the HFN, the strength of both the HFN andthe VLFN and the position of the source in the hard X-ray color vs. intensitydiagram. The frequency of the 97 to 158 Hz Lorentzian does not correlate withthese parameters. We also find that the relation between power density andbreak frequency of the HFN is similar to that established for black holecandidates in the low state. We suggest that the changing mass accretion rateis responsible for the correlated changes in all these parameters.Comment: ApJ, referee