Order sorting and background handling for Arcus

The Arcus X-ray spectrograph (XRS) will deliver high-resolution spectra in four telescope/grating modules (called “channels”) imaged onto the same set of detectors. We examine two effects (cross-dispersion from support structures in the diffraction gratings and frame transfer) that can lead to a photon being assigned to a different channel in the data reduction. Even within a channel, photons can be assigned the wrong diffraction order because orders are closely spaced in energy. Based on simulations, we show that cross-dispersion and frame transfer effects contribute <1% to the extracted signal and that order sorting is efficient enough that only very bright emission lines in a contaminating order can cause a visible signal. Finally, we describe a process to construct per-order non-X-ray background spectra for XRS simulations.