Observed SED (νF_ν) of N (in blue) and S (in red) lobes of 3C 187. Squares represent GMRT fluxes and diamonds represent VLA fluxes. The butterflies indicate the uncertainties on the spectral indices obtained from the power-law fits in the lobes (see Sect. 4.1). The full line butterflies represent the spectral indices obtained with the background subtraction, while the dot-dashed butterflies represent the spectral indices obtained with the background modeling. The full lines represent the simulation of the synchrotron emission, while the dashed lines represent the IC/CMB emission in the same region. The vertical dotted line marks the frequency (∼4 MHz) obtained from Eq. (1) at which the electrons responsible for the IC/CMB radiation at 1 keV emit synchrotron radiation given the magnetic field values shown in Table 4.