Relativistic Thermal Bremsstrahlung Gaunt Factor for the Intracluster   Plasma
  We calculate the relativistic thermal bremsstrahlung Gaunt factor for the high-temperature plasma which exists in clusters of galaxies. We calculate the Gaunt factor by employing the Bethe-Heitler cross section corrected by the Elwert factor. We also calculate the Gaunt factor by using the Coulomb-distorted wave functions for nonrelativistic electrons following the method of Karzas and Latter. By comparing the Gaunt factors calculated by these two different methods, we carefully assess the accuracy of the calculation. We present the numerical results in the form of tables. 
Satoshi Nozawa, Naoki Itoh and Yasuharu Kohyama