Objective Grating Soft X-Ray Spectroscopy of Compact Binary X-Ray Sources

Abstract

The presence of objective transmission gratings on the two recent X-ray telescope experiments, the Einstein and EXOSAT Observatories, has opened up a new avenue of research in X-ray astronomy by enabling us, for the first time, to obtain moderate-to-high resolution spectra of cosmic sources in the soft X-ray band (λ ~ 5–200 Å). Both experiments incorporated gold bar transmission gratings with line densities of 500 1/mm and 1000 1/mm which could be inserted into the X-ray optical path at the exit from a grazing incidence mirror. At short wavelengths, the resolution was determined principally by the spatial resolution of the detector-telescope combination. For Einstein, this was Δλ ~ 0.4 Å for the 1000 1/mm grating and ~ 0.8 Å for the 500 1/mm grating. For EXOSAT, the resolution was somewhat worse: Δλ ~ 1.5 Å for the 1000 1/mm grating, and ~ 3 Å for the 500 1/mm grating. (More complete descriptions of these instruments can be found in Seward et al. 1982 and de Korte et al. 1981.)