In‐Flight Performance of the High Energy X‐Ray Timing Experiment on theRossi X‐Ray Timing Explorer

The High Energy X-ray Timing Experiment (HEXTE) is one of three scientificinstruments aboard the Rossi X-ray Timing Explorer (RXTE), which was launchedon December 30, 1995. RXTE performs timing and spectral studies of bright x-raysources to determine the physical parameters of these systems. The HEXTEconsists of two independent clusters of detectors, each cluster containing fourNaI(Tl)/CsI(Na) phoswich scintillation counters sharing a common 1 degree FWHMfield of view. The field of view of each cluster is switched on- and off-sourceto provide near real-time background measurements. The net open area of theeight detectors is 1600 cm2, and each detector covers the energy range 15-250keV with an average energy resolution of 15.4% at 60 keV. The in-flightperformance of the HEXTE is described, the light curve and spectrum of the CrabNebula/Pulsar is given, and the 15-240 keV spectrum of the weak source, activegalaxy MCG 8-11-11 is presented to demonstrate the weak source spectralcapabilities of HEXTE.Comment: 30 pages, 14 figures, 4 tables, accepted by Ap. J., to be published in vol 496, March 20, 199