On the possibility of observation of X-ray absorption lines in the spectra of BL Lac type objects

The possibility to detect absorption features in the X-ray spectra of quasars and BL Lac type objects, formed in extended radio lobes of these objects is discussed. It is shown that the optical depth in the centre of the strongest absorption lines formed in lobes (O VIII and O VII lines with the energy is not an element of0=0.65 and 0.57 keV respectively as well as C VI and C V lines with is not an element of0=0.37 and 0.31 keV) is τ0 >or approx. 1. The detection of these lines in the X-ray spectra of quasars and BL Lac type objects would give a possibility to estimate directly the temperature and the density of the thermal plasma in these lobes. It is shown that the energy of relativistic electrons is sufficient for plasma heating to the temperature T=107 - 108 K