Using ACIS on the Chandra X-ray Observatory as a particle radiation monitor II

TL;DR

This paper evaluates the effectiveness of using the ACIS instrument on Chandra as a particle radiation monitor by analyzing its response to radiation events and comparing it with external radiation measurements.

Contribution

It introduces a new algorithm that uses CCD data to detect high radiation periods and assesses its performance during radiation events.

Findings

The CCD-based algorithm effectively detects high radiation periods.

The algorithm's efficiency varies with particle flux and spectrum.

ACIS response correlates well with external radiation measurements.

Abstract

The Advanced CCD Imaging Spectrometer is an instrument on the Chandra X-ray Observatory. CCDs are vulnerable to radiation damage, particularly by soft protons in the radiation belts and solar storms. The Chandra team has implemented procedures to protect ACIS during high-radiation events including autonomous protection triggered by an on-board radiation monitor. Elevated temperatures have reduced the effectiveness of the on-board monitor. The ACIS team has developed an algorithm which uses data from the CCDs themselves to detect periods of high radiation and a flight software patch to apply this algorithm is currently active on-board the instrument. In this paper, we explore the ACIS response to particle radiation through comparisons to a number of external measures of the radiation environment. We hope to better understand the efficiency of the algorithm as a function of the flux and spectrum of the particles and the time-profile of the radiation event.