  The High Energy X-ray Timing Experiment (HEXTE) is one of three scientific
instruments aboard the Rossi X-ray Timing Explorer (RXTE), which was launched
on December 30, 1995. RXTE performs timing and spectral studies of bright x-ray
sources to determine the physical parameters of these systems. The HEXTE
consists of two independent clusters of detectors, each cluster containing four
NaI(Tl)/CsI(Na) phoswich scintillation counters sharing a common 1 degree FWHM
field of view. The field of view of each cluster is switched on- and off-source
to provide near real-time background measurements. The net open area of the
eight detectors is 1600 cm2, and each detector covers the energy range 15-250
keV with an average energy resolution of 15.4% at 60 keV. The in-flight
performance of the HEXTE is described, the light curve and spectrum of the Crab
Nebula/Pulsar is given, and the 15-240 keV spectrum of the weak source, active
galaxy MCG 8-11-11 is presented to demonstrate the weak source spectral
capabilities of HEXTE.
