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1. An intrinsic ionized absorber (the zxipcf model) is required by the XMM1 data. Its presence is not statistically significant in any of the other observations, and the model is therefore applied only to the XMM1 spectrum. The XMM1 ionized absorber parameters are NH = (5.2 ± 0.36) × 1021 cm−2 and ionization parameter logξ = 0.35 ± 0.25. The photon index Γ is largely unconstrained by the data above 1–2 keV, so that it is fixed to Γ = 1.8 at all epochs. All fluxes are as observed, and luminosities are unabsorbed. Ldiskbb and LPL are the 0.2–2 keV and 2–10 keV luminosities from the disk and power-law models, respectively. The bolometric luminosity Lbol is estimated from the extrapolation of the best-fitting models down to 10−5 keV (~ 124 μm). The Eddington ratio (Lbol/LEdd) is estimated by assuming a black hole mass of MBH = 4 × 105Mʘ. We note that Lbol (and hence Lbol/LEdd) at the Chandra epoch is considerably more uncertain than that derived from the other observations, as we are effectively fitting a soft excess rather than disk emission (see Methods section ‘Long-term evolution’, where we derive a range of Lbol ≈ (0.09–1.1) × 1043 erg s−1). Errors represent the 90% confidence intervals as obtained from X-ray spectral fits.

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