The temporal characteristics of the Chandra X-ray Observatory high energy particle background

TL;DR

This paper analyzes the variability and temporal patterns of the high-energy particle background in Chandra's ACIS instrument, revealing correlations with orbital position and solar activity over the mission duration.

Contribution

It provides a comprehensive analysis of the high-energy particle background variability and its relation to orbital and solar factors, which was not previously characterized in detail.

Findings

Background flares are cyclic with a quasi-annual period.

Background rates vary on short and long timescales.

Flares correlate with Chandra's orbital position and solar activity.

Abstract

It was observed early on in the Chandra X-ray Observatory mission that the background rates of the Advanced CCD Imaging Spectrometer (ACIS) were highly variable on both short and long timescales. We present analysis of lightcurves of the high energy (> 15 keV) ACIS background spanning most of the mission lifetime. These high energy events are not produced by astrophysical X-rays, but by the particle background, primarily energetic protons. Temporal characteristics of both the quiescent background and background flares will be discussed as well as correlations with Chandra's orbital position and the solar activity cycle. The strength and frequency of background flares appear cyclic with a quasi-annual period, most likely from the motion of Chandra's orbit through the geomagnetic environment.