A Unified Model for GRB Prompt Emission from Optical to Gamma-Rays: Exploring GRBs as Standard Candles

We suggest here to replace the historical spectral model (Band function) for the Gamma-Ray Burst (GRB) prompt emission (keV-MeV energy regime) with a new one. We show that the complex GRB spectral shapes are well described with a combination of three separate components: a thermal-like component and two components with non-thermal spectral shapes. For the first time, analysis of GRBs with correlated optical and gamma-ray prompt emission show that our new model describes very accurately the whole broadband spectrum from the optical regime to higher energy gamma-rays. In addition, this new model enables a new luminosity-hardness relation based on one of the non-thermal component showing that GRBs may be standard candle. If statistically confirmed, this relation will be used to (i) constrain the mechanisms powering GRB jets, (ii) estimate GRB distances, (iii) probe the early Universe, and (iv) constrain the cosmological parameters. I will present this new unified model using analysis of GRBs detected with various observatories and instruments such as Fermi, CGRO/BATSE and the combination of the three instruments on board Swift and Suzaku/WAM. I will discuss here the striking similarities of GRB spectral shapes as well as the possible universality of the proposed luminosity-hardness relation in the context of the new model.