2014MNRAS.444.1829P

High-resolution X-ray spectra of accreting stellar-mass black holes reveal the presence of accretion disc winds, traced by high-ionization Fe K lines. These winds appear to have an equatorial geometry and to be observed only during disc-dominated states in which the radio jet is absent. Accreting neutron star systems also show equatorial high-ionization absorbers. However, the presence of any correlation with the accretion state has not been previously tested. We have studied EXO 0748-676, a transient neutron star system, for which we can reliably determine the accretion state, in order to investigate the Fe K absorption/accretion state/jet connection. Not one of 20 X-ray spectra obtained in the hard state revealed any significant Fe K absorption line. However, intense Fexxv and Fexxvi (as well as a rarely observed Fexxiii line plus Sxvi; a blend of Sxvi and Arxvii; Caxx and Caxix, possibly produced by the same high-ionization material) absorption lines (EW_Fe XXIII-XXV=31±3, EW_Fe XXVI=8±3 eV) are clearly detected during the only soft-state observation. This suggests that the connection between Fe K absorption and states (and anticorrelation between the presence of Fe K absorption and jets) is also valid for EXO 0748-676 and therefore it is not a unique property of black hole systems but a more general characteristic of accreting sources.