NICER SCORPEON Background Model

NICER is an X-ray observatory on the International Space Station, launched in 2017. It consists of 52 independently-operating single-pixel X-ray telescopes. Each of them is calibrated independently to achieve accurate spectral and timing performance in the calibrated energy range of 0.25-10 keV. We present an overview of NICER’s newest background model, called SCORPEON. SCORPEON includes background components for SAA (“S”), cosmic rays (“COR”), polar and trapped electrons (“PE”), constant sky background (“O”) and the noise peak (“N”). SCORPEON provides an a priori background estimate, but also an XSPEC model that can be adjusted to better match NICER spectral data. This approach avoids oversubtraction problems. In addition, the fitted source parameter uncertainties more accurately represents the uncertainties of the background estimate. We present an overview of the SCORPEON technique and its performance.