Accurate determination of the free-free Gaunt factor. II - relativistic Gaunt factors

TL;DR

This paper provides an extensive set of relativistic free-free Gaunt factor tables across a broad parameter space, improving spectral modeling accuracy for ionized plasmas in astrophysics.

Contribution

It introduces the first comprehensive tables of relativistic Gaunt factors over a wide parameter range, merging relativistic and non-relativistic data for improved spectral synthesis.

Findings

Tables cover log10(gamma^2) = -6 to 10 and log10(u) = -16 to 13

Data includes all atomic numbers Z=1 to 36

Tables are publicly available online

Abstract

When modelling an ionised plasma, all spectral synthesis codes need the thermally averaged free-free Gaunt factor defined over a very wide range of parameter space in order to produce an accurate prediction for the spectrum. Until now no data set exists that would meet these needs completely. We have therefore produced a table of relativistic Gaunt factors over a much wider range of parameter space than has ever been produced before. We present tables of the thermally averaged Gaunt factor covering the range log10(gamma^2) = -6 to 10 and log10(u) = -16 to 13 for all atomic numbers Z = 1 through 36. The data were calculated using the relativistic Bethe-Heitler-Elwert (BHE) approximation and were subsequently merged with accurate non-relativistic results in those parts of the parameter space where the BHE approximation is not valid. These data will be incorporated in the next major release of the spectral synthesis code Cloudy. We also produced tables of the frequency integrated Gaunt factor covering the parameter space log10(gamma^2) = -6 to 10 for all values of Z between 1 and 36. All the data presented in this paper are available online.