Annu. Rev. Astron. Astrophys. 1982. 20: 547-85 Copyright © 1982 by Annual Reviews. All rights reserved

1.1 Description of the Einstein Observatory Focal Plane Instruments

The Einstein X-ray telescope observations cover the energy range 0.2-4.5 keV. The Observatory is described in detail by Giacconi et al. (1979); here we briefly summarize the focal-plane instruments and their capabilities.

The high-resolution imager (HRI) provides spatial resolution of ~ 3 arcsec over a field of radius 12 arcmin. It has relatively low quantum efficiency and no intrinsic energy resolution. HRI observations of clusters have been used to map the small-scale structure of the gas and emission from galaxies, as well as to resolve the emission from distant clusters. The imaging proportional counter (IPC) is a moderate-resolution detector (~ 1.5 arcmin). Its advantages, compared to the HRI, include a higher quantum efficiency, moderate energy resolution (E/E ~ 1), less internal background, and a field of view of 1° x 1°. This instrument has been employed extensively for the study of clusters because of their relatively low surface brightnesses.

As there are two complementary imaging detectors, there are two complementary spectroscopic instruments. The solid-state spectrometer (SSS) has moderate spectral resolution, E/E ~ 3-25, and high quantum efficiency. The focal-plane crystal spectrometer (FPCS) has a higher energy resolution (E/E ~ 100-1000) but lower efficiency.