V1223 Sgr and AO Psc Broad Iron Lines
Magnetic cataclysmic variables often show iron K alpha emission lines at 6.4 keV, 6.7 keV, and 6.97 keV from cold (near neutral), helium-like, and hydrogen-like ions, respectively. The ASCA SIS spectrum of the intermediate polar V1223 Sgr is consistent with the presence of three narrow lines at these expected energies. However, the spectrum of AO Psc, a system which is very similar to V1223 Sgr in many respects, taken with the same instrument, is not consistent with three narrow lines. The 6.4 keV line appears narrow but the other lines are clearly broadened. This may be because the lines from the highly ionized ions are resonantly trapped and can only escape the emission region after Compton scattering, which shifts the line energy.
Figure from Hellier, Mukai & Osborne 1998, MNRAS 297, 526.
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