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R. Rutledge (Caltech), L. Bildsten, E. Brown (UCB), G. G. Pavlov (PSU), V. E. Zavlin (MPE-Garching)
A re-analysis of the available quiescent X-ray spectral data of the type-I bursting neutron star transients Aql X-1, Cen X-4, and 4U 1608-522 using realistic hydrogen atmosphere models, instead of the blackbody parameterization, finds the emission surface areas of these consistent with the canonical 10 km radius of a neutron star (whereas the blackbody parameterization does not). Coupled with the recent proposal of a previously neglected energy source (Brown, Bildsten, & Rutledge; ApJ 504 L95) which explains the magnitude of the quiescent luminosity, this suggests that a substantial fraction of the quiescent luminosity is thermal emission from the surface of the neutron star. This has implications for comparisons with black hole quiescent emission, the existence of the so-called "propeller effect", and predicted metal-line emission in these quiescent sources, which should be observable with AXAF and XMM.