X-Ray Emission from Dust in Hot Plasmas

Borkowski, Kazimierz J.; Szymkowiak, Andrew E

Published in: ApJ, 477, 49


Energetic (few keV) thermal electrons easily penetrate interstellar dust grains immersed in hot plasmas. These electrons create K-shell vacancies in atoms locked in dust grains through the K-shell collisional ionization process. Heavy elements such as Fe and Ca produce fluorescent K alpha emission in the subsequent decay of the inner shell vacancy. We predict that this emission from Fe atoms in dust grains should be present in X-ray spectra emitted by dusty plasma, in addition to K alpha emission from highly ionized Fe ions. This affects the strength and shape of the Fe K alpha complex. We also predict a low ratio of L-shell/K alpha emission for dust grains, because of low fluorescent yields for L-shell transitions. These effects should be most pronounced in young supernova remnants (SNRs). We discuss observational evidence for the fluorescent Fe K alpha emission from dust in X-ray spectra of Tycho's, Kepler's, and Cassiopeia A SNRs, the three youngest remnants in our Galaxy.