XMM-Newton RGS observations of MCG-6-30-15 and Mrk 766: evidence for emission lines from a relativistic accretion disk

XMM-Newton Reflection Grating Spectrometer (RGS) spectra of the Narrow Line Seyfert 1 galaxies MCG -6-30-15 and Mrk 766 are 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 Angstrom 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, and we discuss briefly the implications of our interpretation.