X-ray time lags in PG 1211+143

We investigate the X-ray time lags of a recent ∼630 ks XMM–Newton observation of PG 1211+143. We find well-correlated variations across the XMM–Newton EPIC bandpass, with the first detection of a hard lag in this source with a mean time delay of up to ∼3 ks at the lowest frequencies. We find that the energy-dependence of the low-frequency hard lag scales approximately linearly with log(E) when averaged over all orbits, consistent with the propagating fluctuations model. However, we find that the low-frequency lag behaviour becomes more complex on time-scales longer than a single orbit, suggestive of additional modes of variability. We also detect a high-frequency soft lag at ∼10−4 Hz with the magnitude of the delay peaking at ≲ 0.8 ks, consistent with previous observations, which we discuss in terms of small-scale reverberation.