Analytical approximation for the Fe K alpha emission line in quasar spectra

The spectra of many Seyfert galaxies display broad Fe K alpha emission. The line profile has two maxima, suggesting that the line emerges in the innermost regions of an accretion disk around a black hole, making it necessary to take into account general relativistic (GR) effects. Identifying GR processes occuring in active galactic nuclei (AGN) requires reconstructing the parameters of the accreting system from the line profile using some reasonably quick algorithm. We present here a numerical approximation for the Fe K alpha emission line using analytical functions. The approximation encompasses a range of the disk radial coordinate r and the angle plus or minus between the line of sight and the disk normal, and makes it possible to decrease the computing time by six orders of magnitude in certain astrophysical problems, while taking into account all GR effects. Results of the approximation are available at http://www.iki.rssi.ru/people/repin/approx.