X-ray spectroscopy

Abstract

Spectral analysis is the main tool of astrophysical research.Current instrumental technology offers very sensitive CCD detectorswith enough spectral resolution for many purposes.This introductory text is aimed at graduate students starting a thesisin X-ray astronomy, and at non-specialists who wish to analyseX-ray data themselves. It gives the basic tools and explains the basicissues often implicit in specialised papers. X-ray spectroscopy differs from spectroscopy at longer wavelengths because it is photon based with relatively small numbers ofphotons. As a result the Poisson process is at the core of thestatistical description of X-ray spectra. The classicalmodel-fitting procedure is described and illustrated on a detailedexample. It is applicable to any parametric model and anyinstrumental data. High resolution X-ray spectroscopy, now applicable to many sourcesthanks to sensitive grating instruments, allows to measure individuallines accurately. The diagnostics that it offers are very similarto those offered by mid-resolution optical spectroscopy:line ratios, line broadening, absorption lines.