Relativistic thermal bremsstrahlung gaunt factor for the intracluster plasma. II. Analytic fitting formulae

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 less than or equal to Z(j) less than or equal to 28, 6.0 less than or equal to log T less than or equal to 8.5, -4.0 less than or equal to log ((h) over bar omega/k(B) T) less than or equal to 1.0 by combining the relativistic Gaunt factor with the nonrelativistic exact Gaunt factor smoothly, where Z(j) is the charge number of the ion, T is the temperature in kelvins, and omega 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.