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 spectroscop ically inconsistent with standard models comprising a power-law continuum a bsorbed by either cold or ionized matter. We propose that the remarkably si milar features detected in both objects in the 5-35 Angstrom band are H-lik e oxygen, nitrogen, and carbon emission lines, gravitationally redshifted a nd 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.