Proton–synchrotron as the radiation mechanism of the prompt emission of gamma-ray bursts?
G. Ghisellini, G. Ghirlanda, G. Oganesyan, S. Ascenzi, Lara Nava, A. Celotti, O. S. Salafia, M. E. Ravasio, M. Ronchi
Abstract
We discuss the new surprising observational results that indicate quite convincingly that the prompt emission of gamma-ray bursts (GRBs) is due to synchrotron radiation produced by a particle distribution that has a low-energy cut-off. The evidence of this is provided by the low-energy part of the spectrum of the prompt emission, which shows the characteristic Fν ∝ ν1/3 shape followed by Fν ∝ ν−1/2 up to the peak frequency. This implies that although the emitting particles are in fast cooling, they do not cool completely. This poses a severe challenge to the basic ideas about how and where the emission is produced, because the incomplete cooling requires a small value of the magnetic field to limit synchrotron cooling, and a large emitting region to limit the self-Compton cooling, even considering Klein–Nishina scattering effects. Some new and fundamental ingredient is required for understanding the GRBs prompt emission. We propose proton–synchrotron as a promising mechanism to solve the incomplete cooling puzzle.