Introduction

This chapter describes some of the data-analysis methods used by X-ray astrophysicists. Any data analysis must begin with careful consideration of the physics underlying the emission before starting to progress through a series of software tools and scripts. After confirming that existing observations could (at least potentially) answer the question at hand, the first step is to determine what observations of the desired source(s) exist. Recent observations are often the best starting point, but even old data are better than nothing. Once some usable data are available the analysis, either spectral, imaging, timing, or some combination of the three, can proceed.

Low-resolution spectral analysis

General comments

Most recent and current X-ray observations are performed using detectors which provide imaging combined with relatively low spectral resolution. Early missions such as the Einstein Observatory or ROSAT used X-ray mirrors with good imaging capability combined with microchannel plates or position-sensitive proportional counters that had limited spectral sensitivity, typically R ≡ E/ΔE ∼ 1-10. More recent missions, starting with ASCA, and current missions, such as Chandra and XMM–Newton, use X-ray-sensitive CCDs. These tend to have somewhat higher backgrounds, small pixels, and substantially better spectral resolution, R ≡ E/ΔE ∼ 10-50, than proportional counters. For comparison, the standard “UBVRI” optical filter system is equivalent to R ∼ 4.