Erratum: Detection of a second high-velocity component in the highly ionized wind from PG 1211+143

Three publications which were part of the accepted manuscript were omitted from the published version of the above paper (MNRAS 457, 2951, 2016). These are now added below, with the first two providing additional evidence for the existence of more complex structure in active galactic nuclei (AGN) winds. Gupta, Mathur & Krongold (2015) report a Chandra grating observation of the Seyfert galaxy Mrk 590, finding evidence for velocities v ≈ 0.074 c and v ≈ 0.176 c. Longinotti et al. (2015) report an XMM–Newton soft X-ray observation of the Seyfert galaxy IRAS 17020+4544, indicating up to five outflow components with velocities in the range v ≈ 0.079–0.113 c. Shih, Isasawa & Fabian (2002) is an early reference to a double power law being used in the study of spectral variability in AGN.