An explanation about the flat radio spectrum for Mrk 421

It is well known that the flat radio spectrum a common property in spectral energy distribution of blazars. Although one-zone leptonic models are generally successful explaining multi-wave band emission, they problematic reproducing spectrum. In study Mrk 421, suggest order to avoid overproducing flux, minimum electron Lorentz factor should be larger than few hundred at least, even considering synchrotron self-absorption effect. This result suggests model predicted index 421 -1/3. On basis this result, by assuming there neglected region will also contribute emission and its naturally originate from simplest first-order Fermi acceleration mechanism, we can get superimposed paper, two-zone proposed reproduce quiescent state 421. addition taking into account conventional radiation zone, further consider zone which particles accelerated shock front. With present model, our fitting low frequency might explained as superposition zone.