The Nature of the Soft Xray Excess

As an example the new spectral complexity discovered with XMM-Newton and Chandra in the soft X-ray excess components are controversially discussed in the astrophysical community (c.f. Fig. 22.8). [11] explain the soft X-ray excess as rel-ativistically blurred C,O and N lines. In contrast, [30] find that the high resolution soft X-ray spectral feature can be explained by absorption edges, mainly from Fe L, without requiring the line interpretation. [18] pointed out that there might be a potential problem with the line interpretation. Especially the sharpness of the spectral features, which is about 3 eV in the Chandra HETG spectra and about 10 eV in the XMM-Newton RGS data, favours the edge interpretation. This is as the O lines, assuming the line interpretation, are produced in a highly ionized medium with significant Thomson depth and the line is subject to significant line broadening considerable larger than 10 eV. Gravitational redshifts and Doppler motion effects are expected to further broaden the line. More observational and theoretical studies are necessary to solve the puzzle of the soft X-ray spectral complexity.

wavelength [A] energy [keV]

Fig. 22.8 XMM-Newton RGS (left) and Chandra HET (right) spectra of MCG-6-30-15 in the soft energy band. While [11] explain the soft X-ray excess as a superposition of accretion disc lines left, [30] model the spectrum by a combination of absorption edges right. [18] points out that there might be a problem with the line interpretation due to the sharpness of the spectral feature. More observational and theoretical work is required to achieve a better understanding of the nature of the soft X-ray excess wavelength [A] energy [keV]

Fig. 22.8 XMM-Newton RGS (left) and Chandra HET (right) spectra of MCG-6-30-15 in the soft energy band. While [11] explain the soft X-ray excess as a superposition of accretion disc lines left, [30] model the spectrum by a combination of absorption edges right. [18] points out that there might be a problem with the line interpretation due to the sharpness of the spectral feature. More observational and theoretical work is required to achieve a better understanding of the nature of the soft X-ray excess

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