Aims: Drawing an analogy with active galactic nuclei, we investigate the one-zone synchrotron self-compton (SSC) model of gamma ray bursts (GRB) afterglows in the presence of electron injection and cooling both by synchrotron and SSC losses. Methods: We solve the spatially averaged kinetic equations which describe the simultaneous evolution of particles and photons, obtaining the multi-wavelength spectrum as a function of time. We back up our numerical calculations with analytical solutions of the equations using various profiles of the magnetic field evolution under certain simplifying assumptions. Results: We apply the model to the afterglow evolution of GRBs in a uniform density environment and examine the impact various parameters have on the multiwavelength spectra. We find that in cases where the electron injection and/or the ambient density is high, the losses are dominated by SSC and the solutions depart significantly from the ones derived in the synchrotron standard cases.

Recent observations by the H.E.S.S. collaboration of the Galactic Centre region have revealed what appears to be γ-ray emission from the decay of pions produced by interactions of recently accelerated cosmic rays with local molecular hydrogen clouds. Synthesizing a 3D hydrogen cloud map from the available data and assuming a diffusion coefficient of the form κ(E) = κ0(E/E0)δ, we performed Monte Carlo simulations of cosmic ray diffusion for various propagation times and values of κ0 and δ. By fitting the model γ-ray spectra to the observed one we were able to infer the value of the diffusion coefficient in that environment (κ = 3.0 ± 0.2 kpc2 Myr-1 for E = 1012.5 eV and for total propagation time 104 yr) as well as the source spectrum (2.1 ⩽ γ ⩽ 2.3). Also, we found that proton losses can be substantial, which justifies our approach to the problem.

The "Supercritical Pile" is a very economical gamma-ray burst (GRB) model that provides for the efficient conversion of the energy stored in the protons of a relativistic blast wave (RBW) into radiation and at the same time produces—in the prompt GRB phase, even in the absence of any particle acceleration—a spectral peak at energy ~1MeV. We extend this model to include the evolution of the RBW Lorentz factor Γ and thus follow its spectral and temporal features into the early GRB afterglow stage. One of the novel features of the present treatment is the inclusion of the feedback of the GRB produced radiation on the evolution of Γ with radius. This feedback and the presence of kinematic and dynamic thresholds in the model are sources of potentially very rich time evolution which we have began to explore. In particular, one can this way obtain afterglow light curves with steep decays followed by the more conventional flatter afterglow slopes, while at the same time preserving the desirable features of the model, i.e., the well-defined relativistic electron source and radiative processes that produce the proper peak in the νF ν spectra. In this Letter, we present the results of a specific set of parameters of this model with emphasis on the multiwavelength prompt emission and transition to the early afterglow.