TES Based X ray Microcalorimeter Performances Under AC Bias and FDM for Athena
Athena is a European X ray observatory, scheduled for launch in \sim ~2028. Athena will employ a high resolution imaging spectrometer called X ray integral field unit (X IFU) consisting of an array of \sim ~4000 transition edge sensor (TES) microcalorimeter pixels. For the readout of X IFU, we are developing frequency domain multiplexing, which is the baseline readout system. In this paper, we report on the performance of a TES X ray calorimeter array fabricated at Goddard Space Flight Center (GSFC) at MHz frequencies for the baseline of X IFU detector. During single pixel AC bias characterization, we measured X ray energy resolutions (at 6 keV) of about 2.9 eV at both 2.3 and 3.7 MHz. Furthermore, in the multiplexing mode, we measured X ray energy resolutions of about 2.9 eV at 1.3 and 1.7 MHz.