Discovery of Kilohertz Fluctuations in Centaurus X‐3: Evidence for Photon Bubble Oscillations (PBO) and Turbulence in a High‐Mass X‐Ray Binary Pulsar

We report the discovery of kHz fluctuations, including quasi-periodicoscillations (QPO) at ~330 Hz and ~760 Hz and a broadband kHz continuum in thepower density spectrum of the high mass X-ray binary pulsar Centaurus X-3.These observations of Cen X-3 were carried out with the Rossi X-ray TimingExplorer (RXTE). The fluctuation spectrum is flat from mHz to a few Hz, thensteepens to $f^{-2}$ behavior between a few Hz and ~100 Hz. Above a hundred Hz,the spectrum shows the QPO features, plus a flat continuum extending to ~1200Hz and then falling out to ~1800 Hz. These results, which required theco-adding three days of observations of Cen X-3, are at least as fast as thefastest known variations in X-ray emission from an accreting compact object(kHz QPO in LMXB sources) and probably faster since extension to ~1800 Hz isindicated by the most likely parameterization of the data. Multi-dimensional radiation hydrodynamics simulations of optically thickplasma flow onto the magnetic poles of an accreting neutron star show that thefluctuations at frequencies above 100 Hz are consistent with photon bubbleturbulence and oscillations (PBO) previously predicted to be observable in thissource. For a polar cap opening angle of 0.25 radians, we show that thespectral form above 100 Hz is reproduced by the simulations, including thefrequencies of the QPO and the relative power in the QPO and the kHz continuum.This has resulted in the first model-dependent measurement of the polar capsize of an X-ray pulsar.