Effect of different forms of thermal absorption on the radio spectrum of Cas A as well as the fitting of the theoretical dependence to our experimental data obtained with the help of the GURT two-array interferometer (f_a ≈ 0.86). The observations cover the frequency range 16–72 MHz. The black dotted line below our measured spectrum shows the integrated spectrum of Cas A with the parameter values from Arias et al. (2018), where f_a = 0.78 is taken.