A Highly Linear Calibration Metric for TES X-ray Microcalorimeters.

Transition-edge sensor X-ray microcalorimeters are usually calibrated empirically, as the most widely-used calibration metric, optimal filtered pulse height (OFPH), in general has an unknown dependance on photon energy, . Because the calibration function can only be measured at specific points where photons of a known energy can be produced, this unknown dependence of OFPH on leads to calibration errors and the need for time-intensive calibration measurements and analysis. A calibration metric that is nearly linear as a function of could help alleviate these problems. In this work, we assess the linearity of a physically motivated calibration metric, . We measure calibration pulses in the range with detectors optimized for 6 keV photons to compare the linearity properties of to OFPH. In these test data sets, we find that fits a linear function an order of magnitude better than OFPH. Furthermore, calibration functions using , an optimized version of , are linear within the 2-3 eV noise of the data.