All broad-band blazar spectra display two broad and widely separated maxima.
We analyse existing models, which attempt to explain non-thermal emission of blazars addressing the origin of these maxima.
For various reasons that we discuss in this paper, none of these models can claim success with the entire blazar population and rather take responsibility for either GeV or TeV blazars.
In addition, we analyse particle acceleration and radiation processes within joint framework, discuss extreme regimes of radiation and physical limits to the parameters of blazars' emitting zones, and show that in many cases requirements of blazar emission models cannot fit into these fundamental limits.
We also consider recent observation of sub-TeV emission from Gamma-Ray Burst afterglow in the case of GRB 190114C. Derived parameters for the emitting zone of this burst indicate that absorption of sub-TeV radiation inside the emitting zone is an important effect and are in agreement with predictions of the pair-balance model of relativistic shocks.
Based on this evidence, we argue that that relativistic flows (not only in GRBs, but in a general situation as well) are very efficient in accelerating electrons and that the energy of accelerated electrons is limited not by the acceleration process itself, but rather by the back reaction from the high-energy radiation produced in the flow.