2016ApJ...831L...8G

The origin of prompt emission from gamma-ray bursts (GRBs) remains to be an open question. Correlated prompt optical and γ-ray emission observed in a handful of GRBs strongly suggests a common emission region, but failure to adequately fit the broadband GRB spectrum prompted the hypothesis of different emission mechanisms for the low- and high-energy radiations. We demonstrate that our multi-component model for GRB γ-ray prompt emission provides an excellent fit to GRB 110205A from optical to γ-ray energies. Our results show that the optical and highest γ-ray emissions have the same spatial and spectral origin, which is different from the bulk of the X- and softest γ-ray radiation. Finally, our accurate redshift estimate for GRB 110205A demonstrates promise for using GRBs as cosmological standard candles.