Spallation of Iron in Black Hole Accretion Flows

Abstract

In the local Galactic interstellar medium there is approximate energy equipartition between cosmic rays, magnetic fields and radiation. If this holds in the central regions of AGN, in particular Seyfert galaxies, then consideral nuclear spallation of Fe occurs, resulting in enhanced abundances of the sub-Fe elements Ti, V, Cr and Mn. These elements produce a cluster of X-ray flourescence lines at energies just below the 6.4 keV Fe-K$α$ line. It is suggested that the red wings on the Fe lines observed with ASCA from various Seyfert AGN are due to the unresolved line emission from these elements. Future observations with more sensitive X-ray instruments should resolve these lines. The estimated gamma ray emission from nuclear deexcitation and neutral pion production is calculated and found to be below the sensitivities of any current instruments. However, very luminous nearby Seyferts displaying Fe lines with red wings would have $>100$ MeV continuum emission detectable by future instruments such as GLAST.