Speaker
Description
Gamma-ray bursts (GRBs) exhibit remarkable diversity in their prompt emission, yet certain spectral features recur across different events. In this presentation we examine the phenomenon of ultrarelativistic prompt emission (UPE); a short, highly luminous keV–MeV interval characterized by a thermal component superimposed on a nonthermal continuum, in a sample of eight GRBs spanning a wide range of durations and energies. The analysis reveals that this spectral form persists under successive temporal subdivision, establishing an empirical self-similarity in the MeV emission. The recurrent UPE state, observed from the short GRB 090510 to the exceptionally energetic GRB 160625B, provides a robust observational constraint for emission models and points to fundamental physical processes, including pair-plasma transparency and the role of overcritical electromagnetic fields, as key ingredients in the prompt emission mechanism.