Quantifying the Effect of Cosmic Ray Showers on the X‑IFU Energy Resolution

Abstract

The X-ray Integral Field Unit (X-IFU) will operate an array of more than 3000 Transition Edge Sensor pixels at 90 mK with an unprecedented energy resolution of 2.5 eV at 7 keV. In space, primary cosmic rays and secondary particles produced in the instrument structure will continuously deposit energy on the detector wafer and induce fuctuations on the pixels’ thermal bath. We have investigated through simulations of the X-IFU readout chain how these fuctuations eventually infuence the energy measurement of X-ray photons. Realistic timelines of thermal bath fuc tuations at diferent positions in the array are generated as a function of a thermal model and the expected distribution of the deposited energy of the charged particles. These are then used to model the TES response to these thermal perturbations and their infuence on the onboard energy reconstruction process. Overall, we show that with adequate heatsinking, the main energy resolution degradation efect remains minimal and within the associated resolution allocation of 0.2 eV. We further study how a dedicated triggering algorithm could be put in place to fag the rarer large thermal events.