High count rate effects in event processing for XRISM/Resolve x-ray microcalorimeter: I. Ground test

TL;DR

This paper investigates high count rate effects on the XRISM Resolve X-ray microcalorimeter through ground testing, modeling instrumental effects like CPU limits and pile-up to improve high-rate observation accuracy.

Contribution

It introduces models to quantify and mitigate high count rate effects on the microcalorimeter, enhancing its performance during high flux observations.

Findings

Identified key effects: CPU limit, pile-up, electrical cross talk.

Developed models to estimate and correct these effects.

Demonstrated application through simulated observation of GX 13+1.

Abstract

The spectroscopic performance of an X-ray microcalorimeter is compromised at high count rates. In this study, we utilize the Resolve X-ray microcalorimeter onboard the XRISM satellite to examine the effects observed during high count rate measurements and propose modeling approaches to mitigate them. We specifically address the following instrumental effects that impact performance: CPU limit, pile-up, and untriggered electrical cross talk. Experimental data at high count rates were acquired during ground testing using the flight model instrument and a calibration X-ray source. In the experiment, data processing not limited by the performance of the onboard CPU was run in parallel, which cannot be done in orbit. This makes it possible to access the data degradation caused by limited CPU performance. We use these data to develop models that allow for a more accurate estimation of the aforementioned effects. To illustrate the application of these models in observation planning, we present a simulated observation of GX 13+1. Understanding and addressing these issues is crucial to enhancing the reliability and precision of X-ray spectroscopy in situations characterized by elevated count rates.