The COSI Science Data Pipeline

The Compton Spectrometer and Imager (COSI) is a NASA Small Explorer mission (SMEX) scheduled to be launched in 2027. COSI will study the soft gamma-ray sky (0.2-5 MeV) and observe astrophysical sources of nuclear-line emission, reveal the origins of Galactic positrons, measure the polarization of gamma-ray bursts (GRBs), accreting black holes, and pulsars, as well as detect and localize multimessenger sources. COSI’s science data analysis pipeline consists of three main stages: The first stage processes the downlinked data from raw information in AD units, strip & detector IDs, timings, etc. to interaction positions and energies in its Germanium detectors. The second stage reconstructs the parameters of the initial Compton interaction for each event and determines its quality. The third stage utilizes the Compton events and enables scientific analysis such as generating spectra, images, light curves, etc. During normal operations, this pipeline can run fully automatically. For example, after data downlink via TDRSS, it can analyze on-board detected short transients, and, within less than 1 hour of detection, publish their location via GCN. The pipeline will also generate updated light curves and spectra of known bright sources at regular intervals, along with all-sky images in different energy bands. Additionally, the pipeline will provide a comprehensive set of tools to fully analyze all aspects of the data that COSI will measure. All data will be made public as soon as it is verified, typically within one week. The first six months in orbit are an exception, as this period will be dedicated to verifying and, if necessary, correcting the on-orbit instrument response, as well as creating an on-orbit background model. Before launch, the COSI team plans to conduct yearly data challenges, offering a few months of simulated data for analysis with the latest version of the pipeline. This initiative provides the high-energy community with an opportunity to gain a better understanding of the COSI data analysis. Additionally, it allows the community to provide feedback on the pipeline development to the COSI pipeline team. Data Challenge 2 is scheduled for release ahead of the 2024 HEAD meeting.