The X-ray Integral Field Unit (X-IFU) on the NewAthena X-ray Observatory will fly a 1,504 pixel transitionedge sensor (TES) microcalorimeter array to study the Hot and Energetic X-ray Universe. For the first time, we have developed and measured a flight-like X-IFU detector that matches the pixel design and array configuration of the planned flight model, including the now baselined 50μm × 30μm TES pixels as well as flight-like electrical and mechanical wafer interfaces. This detector has undergone detailed characterization at NASA/GSFC in preparation to serve as the Development Model (DM) array for the X-IFU instrument. We measured roughly 150 pixels distributed across the ∼1.5 cm diameter hexagonal detector array to verify target adherence and spatial uniformity of key TES pixel parameters and performance metrics, including transition temperature, transition shape, normal-state resistance, conductance to thermal bath, complex impedance, and spectral resolution. The average spectral resolution at 6.9 keV is 2.01 ± 0.31 eV, or 1.93 ± 0.11 eV when removing 16 pixels with degraded performance from fabrication defects. For a smaller subset of pixels we also verified the pixel crosstalk and gain sensitivities meet requirements.
Hull et al. (2026) studied this question.