PG 1211+143: probing high frequency lags in a high mass AGN
  We present the timing analysis of the four archived XMM-Newton observations of PG 1211+143. The source is well-known for its spectral complexity, comprising a strong soft-excess and different absorption systems. Soft energy band (0.3-0.7 keV) lags are detected over all the four observations, in the frequency range $\nu \lsim 6 \times 10^{-4}$ Hz, where hard lags, similar to those observed in black hole X-ray binaries, are usually detected in smaller mass AGN. The lag magnitude is energy-dependent, showing two distinct trends apparently connectable to the two flux levels at which the source is observed. The results are discussed in the context of disk- and/or corona-reprocessing scenarios, and of disk wind models. Similarities with the high-frequency negative lag of 1H 0707-495 are highlighted, and, if confirmed, they would support the hypothesis that the lag in PG 1211+143 represents the signature of the same underlying mechanism, whose temporal characteristics scale with the mass of the central object. 
B. De Marco, G. Ponti, P. Uttley, M. Cappi, M. Dadina, A. C. Fabian,   G. Miniutti
astro-ph.HE