Detection of a broad iron emission line and sub-millisecond quasiperiodic oscillations from the type I X-ray burster 4U 1728-34 in a high state

We report results from simultaneous RossiXTE and BeppoSAX observations of t he neutron-star x-ray binary and type I X-ray burster 4U 1728-34. The sourc e was found in a high luminosity state, L-X similar to 0.1L(Edd), and quasi periodic oscillations were detected at 1284+/-6 Hz, the highest frequency e ver observed from this source. The x-ray spectrum shows a broad, FWHM simil ar to 0.8 keV, iron K-alpha fluorescence line. We discuss interpretations o f the broad line and the quasiperiodic oscillations and how future simultan eous spectral and timing observations can be used to test these interpretat ions and, potentially, to estimate the mass of the compact object.