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Durham University

Department of Physics

Staff profile

Publication details for Prof Chris Done

Alston, W.N., Done, C. & Vaughan, S. (2014). X-ray time delays in the narrow line Seyfert 1 galaxy PG 1244+026. Monthly Notices of the Royal Astronomical Society 439(2): 1548-1555.

Author(s) from Durham


We analyse the X-ray time-lags in the narrow line Seyfert 1 (NLS1) galaxy PG 1244+026 (MBH ∼ 107 M⊙, L/LEdd ∼ 1). The time delay between the soft (0.3–0.7 keV) and harder (1.2–4.0 keV) variations shows the well-established switch from hard lags at low frequencies to soft lags at high frequencies. The low-frequency hard lags are qualitatively consistent with the propagation of fluctuations model, with some long-time-scale response of the reflection component. The high-frequency soft lag appears to extend over a wide frequency band, that we divide this into two narrow frequency ranges, and examine the lag as a function of energy for each of these. At high frequencies the soft excess emission is delayed with respect to the harder energy bands, without any corresponding strong, hard X-ray reflection signature. At even higher frequencies a soft lag is seen at the softest energies, as well as tentative evidence for an iron Kα reverberation signal. These results point to the importance of reprocessing as well as reflection in determining the lags in NLS1s.