2020ApJ...903L..26H

Bimodal spectral energy distributions (SEDs) of gamma-ray burst (GRB) afterglow of GRBs 190114C, 130427A, and 180720B confirm that they are originated from the synchrotron emission (Syn) and synchrotron self-Compton scattering (SSC) process of electrons accelerated in the jets. The radiation mechanism and the physics of the observed spectrum-luminosity/energy relations of GRBs remain as open questions. By extracting the Syn component through fitting their early afterglow SEDs with the Syn+SSC model, we find that their luminosity (L_syn), peak energy (E_p,syn,z), and the Lorentz factor of the afterglow fireball (Γ_t) follow the L_p,iso-E_p,z-Γ₀ relation of prompt gamma rays, where L_p,iso is the isotropic luminosity, E_p,z is the peak energy of the νf_ν spectrum in the burst frame, and Γ₀ is the initial Lorentz factor of the fireball. To examine whether late afterglows are consistent with this relation, we calculate the synchrotron component at late afterglows. It is found that they also follow the same L_p,iso-E_p,z-Γ₀ relation, albeit they are not consistent with the L_p,iso-E_p,z relation. Our results may imply that the L_p,iso-E_p,z-Γ₀ relation would be a universal feature of synchrotron radiations of electrons accelerated in GRB jets throughout the prompt and afterglow phases among GRBs. Its origin is not fully understood, and possible explanations are briefly discussed.