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A 57 Fe nucleus in the solar core could emit a 14.4-keV monochromatic axion through the M1 transition if a hypothetical elementary particle, axion, exists to solve the strong CP problem. Transition edge sensor (TES) X-ray microcalorimeters can detect such axions very efficiently if they are again converted into photons by a 57 Fe absorber. We have designed and produced a dedicated TES array with 57 Fe absorbers for the solar axion search. The iron absorber is set next to the TES, keeping a certain distance to reduce the iron-magnetization effect on the spectroscopic performance. A gold thermal transfer strap connects them. A sample pixel irradiated from a 55 Fe source detected 698 pulses. In contrast to thermal simulations, we consider that the pulses include either events produced in an iron absorber or gold strap at a fraction dependent on the absorption rate of each material. Furthermore, photons deposited on the iron absorber are detected through the strap as intended. The identification of all events still needs to be completed. However, we successfully operated the TES with the unique design under iron magnetization for the first time. [ABSTRACT FROM AUTHOR]

This study attempted to develop detection methods for solar axions using transition-edge-sensor (TES) microcalorimeters. Since the axion absorber comprised of iron-57 (57Fe) is electroplated upon the membrane instead of directly onto the TES itself (with the absorber hence thermally connected to the TES via a gold thermal strap), some of the heat deposited into the absorber consequently escapes into the heat bath through the membrane before being detected by the TES. If the heat-loss depends upon the axion interaction position within the absorber, position dependence may degrade the energy resolution. Therefore, this study endeavored to evaluate the dependence of heat-loss and pulse shape on axion incident position with the COMSOL Multiphysics software package (using a finite element method). In addition, heat-loss and pulse shape were likewise evaluated when the energy was deposited directly within the gold thermal strap. [ABSTRACT FROM AUTHOR]