Orateur
Description
CMB (Cosmic Microwave Background) spectral distortions can probe the thermal and energetic history of the early Universe. However, the CMB spectrum has not been remeasured since COBE/FIRAS, which constrained deviations from a blackbody to ΔI/I ≲ 10⁻⁵. Detecting these faint signals requires anticipating, from the earliest design stages, how instrumental systematics will limit the measurement.
We present our study of systematic effects for FOSSIL (FTS fOr CMB Spectral diStortIon expLoration) and BISOU (Balloon Interferometer for Spectral Observation of the Universe), a Fourier-transform spectrometer (FTS) designed to probe spectral distortions. First, the instrument was modeled with the TICRA GRASP software, which allows us to model the optical aberrations and the systematics introduced by the moving mirror of the FTS. Then, we present our instrument simulator, which will be able to forecast the error induced on the science measurement by optical systematics. To validate these predictions, a laboratory breadboard of the instrument is being built at the Institut d'Astrophysique Spatiale (IAS), which will allow us to characterise these systematics experimentally and compare them with the simulator, a key step towards the validation of the model ahead of the mission.