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R.I. Klein (University of California, Berkeley Dept. of Astronomy and Lawrence Livermore National Laboratory), J.G. Jernigan (University of California, Space Science Laboratory)
We present the first time-dependent, multi-dimensional, radiation hydrodynamical calculations of the plasma flow of super-Eddington accreting neutron stars through hollow cone accretion columns. Applications of hollow cone models for realistic sources will be estimated for detection on the RXTE PCA and for large apertures of order 105 cm2 (10 X PCA). Filled accretion columns are expected when accretion occurs from a wind or from a thick disk. In thin disk accretion, however, one encounters hollow cones, an extreme form of transverse structure in the polar accretion flow. In this instance, the field lines connected to the center of the pole are likely to be open, with the matter crossing the inner boundary layer of the disk onto the field lines whose stellar foot print forms a partial or complete ring around the magnetic axis. Such a configuration is extremely interesting, since the optically thick walls of the accretion ``funnel'' can force the radiation emitted into the hollow interior of the column to emerge as a radiation pencil beam or jet. We will present new results for a range of values of accretion luminosity, surface magnetic field, and polar cap extent and study the emergent light curve and beaming profile of hollow cone accretion with particular attention to the formation of pencil beams versus fan beams in an accreting X-ray pulsar. We will discuss the possible acceleration of a radiation driven plasma jet from the accretion column. The properties of Photon Bubble Oscillations (PBO) in hollow cone accreting X-ray pulsars will be contrasted with the characteristic millisecond fluctuations(oscillations) discovered in uniformly filled X-ray pulsar accretion columns. Detection and measurment of pulse resolved PBO effects and individual flares in the time varying luminosity may be possible with next generation large aperture x-ray timimg detectors.
This work was partially supported under the auspices of the US Department of Energy at LLNL under contract W-7405-Eng-48.