We report results from simultaneous RossiXTE and BeppoSAX observations of the neutron-star x-ray binary and type I X–ray burster 4U 1728-34 .
The source was found in a high luminosity state , L _ { X } \sim 0.1 L _ { Edd } , and quasiperiodic oscillations were detected at 1284 \pm 6 Hz , the highest frequency ever observed from this source .
The x-ray spectrum shows a broad , FWHM \sim 0.8 keV , iron K _ { \alpha } fluorescence line .
We discuss interpretations of the broad line and the quasiperiodic oscillations and how future simultaneous spectral and timing observations can be used to test these interpretations and , potentially , to estimate the mass of the compact object .