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R. E. Rutledge (Caltech), L. Bildsten (ITP/UCSB), E. F. Brown (UChicago), G. G. Pavlov (PSU), V. E. Zavlin (MPE)
We report on XMM observations of the transient neutron star low-mass X-ray binary Cen X-4, in quiescence. The X-ray source in quiescence exhibits intensity variability (42+/-4% rms), significantly stronger than the upper-limit on variability obtained with Chandra (<18% rms, 3 sigma). Interestingly, the spectra of the highest and lowest intensity periods are consistent with having the same components (an absorbed H atmosphere plus power-law). However, the difference in the spectra cannot be accommodated by a change in (only) the power-law component, nor in the absorption, or in the effective radius. The difference can, however, be accommodated by a changing effective temperature alone. We will discuss these results in the context of deep crustal heating and accretion models for powering the quiescent emission, and their implications for neutron star radius measurements.
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Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.