The High Energy X-ray Timing Experiment

The HEXTE consists of two independent clusters each of 4 detectors for measuring x-rays from 10 to 200 keV. Each HEXTE cluster consists of a mounting structure that attaches to the RXTE spacecraft and an array of 4 detector units (each containing a collimator, phoswich detector, photomultiplier tube, gain control detector and associated electronics). These detector units are mounted on a shaft which can rotate them to either ±1.5° or ±3.0° about the nominal source-pointing direction of RXTE. The two clusters are oriented such that the axes of their rocking motions are mutually orthogonal, while the on-source look directions are co-aligned. This enables the sampling of four background positions on the sky around the the source-pointing direction.

The HEXTE was designed, built and tested at the Center for Astrophysics & Space Sciences, at the University of California, San Diego, where the HEXTE Principal Investigator is Dr. Richard Rothschild.

[CEU] [Shields] [Phoswich Detector Assemblies] [Rocking Mechanism]

Photographs: top view

HEXTE properties

Characteristic	Value
Energy range	12-250 keV in 256 channels
Energy resolution	dE/E ~ E^-0.5; =15% at 60 keV
Time sampling	7.6 µs (maximum)
Field-of-view	2.2° FWZI (FWHM response=1°)
Detector material	NaI(Tl), CsI(Na)
Net detector area	2 × 890 cm²
Live-time fraction on-source	60%
Count rate from Crab Nebula (12-250 keV)	250 count/s per cluster
Count rate from internal background (12-250 keV)	90 count/s per cluster
Detection sensitivity in 10⁵ s, 3sigma	10^-6 photons/cm² s keV at 100 keV
Source/background dwell time	16 to 128 s
Calibration source	²⁴¹Am (lines at 17 and 60 keV)
Gain variation	<1%
Detector operating temperature	17-27 °C
Weight	390 kg
Operational power	45 W
Allocated telemetry rate	5000 bit/s (average)

Next stop: Learn more about the HEXTE detector assemblies

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