Extended Line Spread Function of TES Microcalorimeters With Au/Bi Absorbers

Abstract

Microcalorimeters have the potential to provide line shapes well described by a single Gaussian broadening term of few-eV width. This attribute makes the detectors especially well suited for x-ray astrophysics observations; however, low-level non-Gaussian broadening terms are expected and must be characterized. These terms depend on the composition of the x-ray absorber, the detailed x-ray absorption physics, the device thermalization processes, and the incident x-ray energy. Here we present the first measurements targeted at understanding the extended line-spread function (LSF) of x-ray microcalorimeter pixels under development for the X-ray Integral Field Unit on the Athena X-ray Observatory. These pixels are composed of Mo/Au transition-edge sensors with overhanging electroplated Au/Bi absorbers. We have measured the line shapes using monochromatic x-ray sources with <1-eV width at several x-ray energies (0.85, 0.93, 1.25, 1.5, 5.4, and 8.0 keV) across the instrument bandpass (0.3–12 keV) and have modeled the line profiles. These results are compared to the extended LSF of the Hitomi microcalorimeter pixels that used HgTe absorbers.