PANDORA: New avenues in sub-percent photometric precision for ground based astronomy

Abstract: Precision photometric calibration is key to a number of astrophysical research areas such as supernova cosmology and dark energy studies. In the age of large surveys, pushing the limits of photometry is a worthy challenge, with traditional celestial calibrators limited to approximately percent precision. Here we present PANDORA, a novel calibration source that achieves sub-percent photometric precision across the optical spectrum with a selectable dynamic range and high optical efficiency. Building on proven collimated beam projector designs for relative throughput calibration of survey telescopes, PANDORA is capable of delivering photons anywhere in the 350-1100 nm spectral range. It uses selectable neutral density filters and sequential NIST-calibrated photodiode feedback to internally self-calibrate prior to operation, and is illuminated by an Energetiq EQ-99X-FC broadband laser-driven light source. We present here an overview of the system design, operation, and laboratory characterization results. PANDORA will begin science operations this year to support the upcoming LS4 survey on the ESO 1m Schmidt telescope.