Towards a 3D analysis in Cherenkov γ -ray astronomy

The development of a 3D or cube analysis to simultaneously fit a spectral and morphological model to the data is a challenge in Cherenkov gamma-ray astronomy. The strong variation of the instrument response functions and of the residual cosmic rays background with the observation conditions makes it very difficult to build a coherent background model across the whole energy range. Nevertheless, with improving sensitivities and angular resolution of current Cherenkov telescopes and next generation instruments such as the Cherenkov Telescope Array, the complex morphology of the regions with diffuse emission or multiple sources requires the development of this technique. We developed a prototype for cube analysis along with corresponding background models for varying observations conditions. The prototype as well as the production of background model was implemented in the software Gammapy, an open source Python package for gamma-ray Astronomy that provides tools to simulate and analyse the gamma-ray sky for imaging atmospheric Cherenkov telescopes. To validate the method, we performed a systematic comparison between this cube analysis and the classical 1D spectral fitting on point sources using a Monte Carlo simulation from the H.E.S.S. collaboration.