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Session 110 - X-ray, Binaries & Accretion Disks.
Display session, Saturday, January 10
Exhibit Hall,
We present initial results of a study of the continuum x-ray spectra (2-100 keV) of low mass x-ray binaries (LMXBs) in which the neutron star (NS) primary accretes from a white dwarf (WD) secondary. Two such ultra-compact LMXBs have been observed with RXTE: 4U1916-05, a 50-min binary period system in the galactic disk, and 4U1820-30, the 11-min binary in the core of the globular cluster NGC 6624. Both are x-ray bursters and both systems show long-term variations (with possible periods of \sim199d and 176d, respectively) of their 2-10 keV flux. Our RXTE spectral studies are designed to measure: i) the continuum spectrum and the spectral break energy, E_b, of the hard x-ray tail, ii) the variation of the measured spectral parameters with both orbital and long-term phase, and iii) the dependence of the hard x-ray spectral component and break energy E_b on total flux and accretion rate. Data from the PCA and HEXTE detectors are used to constrain spectral fits, while ASM data provide long-term intensity state monitoring. Results from our long-term study of 4U1916-05 will be presented in some detail, and compared with our initial results for 4U1820-30, in an effort to constrain the origin of hard x-ray emission in LMXBs.
