XMM-Newton RGS spectroscopy of the M31 bulge. I: Evidences for a past AGN half a million years ago

Shuinai Zhang, Q. Daniel Wang, Adam R. Foster +3

Existing analysis based on XMM-Newton/RGS spectra already shows that the G-ratio of the OVII He$\alpha$ triplet in the inner bulge of M31 is too high to be consistent with a pure optica…