Initial characterization of the soft X-ray spectral resolution of back-illuminated CMOS sensors for solar physics

Current solar soft X-ray (SXR) satellite observatories perform measurements in either of two regimes: (1) spatially integrated and spectrally resolved measurements or (2) spatially separated and spectrally integrated via a filter. The combination of imaging spectral measurements from a satellite platform does not exist. We, at the Smithsonian Astrophysical Observatory (SAO), are testing silicon-based CMOS detectors as a baseline for future solar SXR missions to perform spatial and spectrally resolved measurements. Silicon-based CMOS sensors offer higher intrinsic dispersive energy resolution than previously used germanian sensors and higher speed readout capabilities than current CCD detectors. This allows for higher resolution spectral imaging and higher dynamic range than previous solar physics SXR detectors. SAO and SRI International have developed back-illuminated CMOS detectors for SXR direct detection, combined with high gain pixels with relatively lower noise. We provide insight on current development of SAO/SRI CMOS detector spectral resolution in response to 55Fe characteristic x-ray emission spectra, namely the K-⍺ and K- emission lines at 5.9 keV and 6.4 keV, respectively. Through the statistical analysis of Gaussian model fitting, we characterized the CMOS detector response to these 55Fe emission lines. This research is funded through NASA grant number 80NSSC20K0919 and NSF-REU Solar Physics Program@SAO AGS-1850750