Rxte (pronounced “rocks-tee”) is a powerful X-ray satellite observatory, launched on December 30, 1995. Rxte was designed to study X-ray sources with unprecedented sensitivity and resolution, in order to understand the physics of these objects. The satellite carries three main instruments: the All-Sky Monitor (ASM), the Proportional Counter Array (PCA), and the High Energy X-ray Timing Experiment (HEXTE).
The ASM consists of an array of scanning shadow cameras which continuously monitor about 75% of the sky for transient X-ray sources. The PCA is a set of five large area proportional counters with good energy resolution, which together provide simultaneous coverage over a wide energy band (2 – 60 keV). The HEXTE is comprised of two clusters of four NaI(Tl)/CsI(Na) phoswich scintillation detectors, which extend the energy range covered by the PCA out to 250 keV.
Since its launch, Rxte has observed thousands of X-ray binaries, black hole candidates, neutron star systems, active galactic nuclei, supernova remnants, and other objects. In doing so, it has made many important discoveries about the nature of these objects. For example, Rxte was key in showing that some black hole candidates exhibit quasi-periodic oscillations (QPOs) in their X-ray flux; these QPOs are thought to be caused by disk material orbiting close to the event horizon of the black hole. Additionally, Rxte’s data have been used to map out detailed structures within accretion disks around black holes and neutron stars.