Multiabsorber transition-edge sensors for x-ray astronomy

Abstract. We are developing arrays of position-sensitive microcalorimeters for future x-ray astronomy applications. These position-sensitive devices commonly referred to as hydras consist of multiple x-ray absorbers, each with a different thermal coupling to a single-transition-edge sensor microcalorimeter. Their development is motivated by a desire to achieve very large pixel arrays with some modest compromise in performance. We report on the design, optimization, and first results from devices with small pitch pixels (<75  μm) being developed for a high-angular and energy resolution imaging spectrometer for Lynx. The Lynx x-ray space telescope is a flagship mission concept under study for the National Academy of Science 2020 decadal survey. Broadband full-width-half-maximum (FWHM) resolution measurements on a 9-pixel hydra have demonstrated ΔEFWHM  =  2.23  ±  0.14  eV at Al-Kα, ΔEFWHM  =  2.44  ±  0.29  eV at Mn-Kα, and ΔEFWHM  =  3.39  ±  0.23  eV at Cu-Kα. Position discrimination is demonstrated to energies below <1  keV and the device performance is well-described by a finite-element model. Results from a prototype 20-pixel hydra with absorbers on a 50-μm pitch have shown ΔEFWHM  =  3.38  ±  0.20  eV at Cr-Kα1. We are now optimizing designs specifically for Lynx and extending the number of absorbers up to 25/hydra. Numerical simulation suggests optimized designs could achieve ∼3  eV while being compatible with the bandwidth requirements of the state-of-the art multiplexed readout schemes, thus making a 100,000 pixel microcalorimeter instrument a realistic goal.