The possibility of observing X-ray absorption lines in the spectra of quasars

The possibility of observing, in the spectra of quasars, X-ray absorption lines formed in the hot plasma in objects lying in the line of sight is discussed. It is shown that for typical parameters of the hot plasma in rich clusters and the coronas of giant galaxies, the equivalent widths of such lines in the spectra of ordinary quasars barely exceed 50 eV. To detect these lines, the spectral sensitivity of instruments would have to be increased by a factor of at least 10. The most probable transitions are given for the most abundant heavy elements, and it is noted that attempts at detecting these transitions could be made even now with the aid of instruments on board the Einstein Observatory.