Soft X-ray emission lines from a relativistic accretion disk in MCG   -6-30-15 and Mrk 766
  XMM-Newton Reflection Grating Spectrometer (RGS) spectra of the Narrow Line Seyfert 1 galaxies MCG -6-30-15 and Mrk 766 are physically and spectroscopically inconsistent with standard models comprising a power-law continuum absorbed by either cold or ionized matter. We propose that the remarkably similar features detected in both objects in the 5 - 35 A band are H-like oxygen, nitrogen, and carbon emission lines, gravitationally redshifted and broadened by relativistic effects in the vicinity of a Kerr black hole. We discuss the implications of our interpretation, and demonstrate that the derived parameters can be physically self-consistent. 
G. Branduardi-Raymont (1), M. Sako (2), S. M. Kahn (2), A. C. Brinkman   (3), J. S. Kaastra (3), M. J. Page (1) ((1) Mullard...