Multi-epoch spectroscopy of the globular cluster black hole in NGC 4472

We present a study of the X-ray spectral properties of the highly variable X-ray emitting black hole in a globular cluster in the elliptical galaxy NGC 4472. The X-ray Multiple Mirror-Newton (XMM-Newton) spectrum of the source in its bright epoch is well described by a multiple blackbody model with a characteristic temperature kT_in ≈ 0.2 keV. The spectrum of an archival Chandra observation of the source obtained 3.5 yr before the XMM data gives similar estimates for the blackbody parameters. We confirm that the fainter interval of the XMM-Newton observation has a spectrum that is consistent with the brighter epoch, except for an additional level of foreground absorption. We also consider other possible mechanisms for the variability. Based on the time-scale of the X-ray flux decline and the estimated size of the X-ray emission region, we argue that an eclipsing companion is highly unlikely. We find the most likely means of producing the absorption changes on the observed time-scale is through partial obscuration by a precessing warped accretion disc.