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

TL;DR

This paper investigates the potential of using the ACIS CCDs on the Chandra X-ray Observatory as an onboard particle radiation monitor by analyzing a decade of data to improve radiation protection strategies.

Contribution

It introduces a novel approach of utilizing existing CCDs as radiation monitors, enhancing autonomous protection amid aging insulation and reduced effectiveness of current systems.

Findings

ACIS CCDs respond reliably to particle radiation levels.

Correlation established between CCD data and other radiation environment models.

Potential for improved autonomous radiation protection using CCDs.

Abstract

The Advanced CCD Imaging Spectrometer (ACIS) is one of two focal-plane instruments on the Chandra X-ray Observatory. During initial radiation-belt passes, the exposed ACIS suffered significant radiation damage from trapped soft protons scattering off the x-ray telescope's mirrors. The primary effect of this damage was to increase the charge-transfer inefficiency (CTI) of the ACIS 8 front-illuminated CCDs. Subsequently, the Chandra team implemented procedures to remove the ACIS from the telescope's focus during high-radiation events: planned protection during radiation-belt transits; autonomous protection triggered by an on-board radiation monitor; and manual intervention based upon assessment of space-weather conditions. However, as Chandra's multilayer insulation ages, elevated temperatures have reduced the effectiveness of the on-board radiation monitor for autonomous protection. Here we investigate using the ACIS CCDs themselves as a radiation monitor. We explore the 10-year database to evaluate the CCDs' response to particle radiation and to compare this response with other radiation data and environment models.