Detection of Sharp Spectral Drops Above 7 keV

One of the most interesting spectral features detected with XMM-Newton is probably the discovery of sharp spectral power-law cut-offs at the Fe K edge energy as observed in the NLS1s 1H 0707-495 ([6,21]) and IRAS 13224-3809 ([7]; c.f. Fig. 22.6).

channel energy (keV)

channel energy (keV)

Fig. 22.6 Left: XMM-Newton spectrum of 1H 0707-495 obtained in October 2000. A sharp spectral drop at the energy of the neutral Fe K edge at 7.1 keV has been detected. Right: XMM-Newton spectrum of IRAS 13224-3809. The sharp spectral drop occurs at even higher energies at 8.2 keV

1 For a qualitative discussion on the intensity variations caused by the relativistic Doppler effect, a approximation to a simple power law model is sufficient. The apparent intensity variations in the observers frame are mainly caused by a frequency shift of the emitted radiation in the ROSAT energy band. The steepness of the X-ray continuum slope is dominant with respect to the exact form of the spectral energy distribution.

A possible interpretation is an absorption model. The missing Fe K re-emission can be explained by a partial covering model ([6,27,50]). The partial covering model requires high densities of the absorber, located in the accretion disc environment. As they substain only a small solid angle, the Fe K re-emission remains undetected with the present generation of X-ray telescopes. In the partial covering scenario a part of the emission from the accretion disc reaches the absorber unabsorbed giving rise to the strong soft X-ray excess.

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