Spectral and Timing Performance of COSI’s Front-end ASIC

The Compton Spectrometer and Imager (COSI) NASA Small Explorer mission is a Compton telescope designed to study MeV astrophysics, slated for launch in 2027. COSI’s main science goals include mapping the Galactic 511 keV emission and radioactive elements from nucleosynthesis, studying source geometries and magnetic fields of compact objects through polarization measurements, and detecting and studying gamma ray bursts. The heart of COSI consists of 16 high purity germanium double-sided strip detectors, through which we can perform imaging, spectroscopy, and polarimetry of astrophysical sources by precisely measuring the interaction position and energy deposited during each photon interaction. To read out the germanium detectors, we have developed a front-end application specific integrated circuit (ASIC) that preserves the energy resolution inherent to germanium while also performing precise timing measurements that allow for determining the depth of interaction in the detector. Here we present the spectral and timing performance of the front-end ASIC, evaluated both on the bench and on a detector similar to the COSI flight detectors, and show that the ASIC meets the specifications needed for COSI to perform its science goals.