http://arxiv.org/abs/1602.05158
We have analyzed five archived X-ray observations of NGC~4051 taken using the NuSTAR observatory. The data show lags between flux variations in bands of different X-ray photon energy. In all pairs of bands compared, the harder band consistently lags the softer band by at least 1000s, at temporal frequencies ~5 x 10^-5 Hz. In addition, soft-band lags up to 400s are measured at temporal frequencies ~2 x 10^-4 Hz. Light echos from the inner accretion disk cannot explain the lags in these data, as a sharp soft-band lag is seen in cross-correlations where the softer band is expected to have no contribution from reflection. We find a simple top hat model to be consistent with the response function producing the reprocessed signal. The scattered fraction of X-rays is high, indicating the reprocessor to have a global covering fraction ~50% around the continuum source. The scattered fraction increases with increasing photon energy, while the maximum time delay decreases. Such a scenario may be explained by a higher fraction of the soft photons being scattered from large radii relative to the hard photons. A stratified clumpy wind provides a compelling physical model that satisfies all observational criteria.
T. Turner, L. Miller, J. Reeves, et. al.
Wed, 17 Feb 16
29/55
Comments: 8 pages, 4 figures. Submitted to MNRAS
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