Relativistic Thermal Bremsstrahlung Gaunt Factor for the Intracluster Plasma. II. Analytic Fitting Formulae

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Abstract
We present accurate analytic fitting formulae that summarize the results of the recent calculation by Nozawa, Itoh, & Kohyama on the relativistic thermal bremsstrahlung Gaunt factor for the intracluster plasma. The fitting is carried out for 1 ≤ Zj ≤ 28, 6.0 ≤ log T ≤ 8.5, -4.0 ≤ log(ω/kBT) ≤ 1.0 by combining the relativistic Gaunt factor with the nonrelativistic exact Gaunt factor smoothly, where Zj is the charge number of the ion, T is the temperature in kelvins, and ω is the angular frequency of the emitted photon. We also present an accurate analytic fitting formula for the nonrelativistic exact Gaunt factor. This fitting formula is best suited for relatively low-temperature plasmas in which the relativistic effect is negligible. The present analytic fitting formulae will be useful for the analysis of the X-ray emission which comes from the intracluster plasma as well as thef other X-ray sources.

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