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NGC 4151 is the brightest Seyfert 1 nucleus in X-rays. It was the first object to show short time delays in the Fe K band, which were attributed to relativistic reverberation, providing a new tool for probing regions at the black hole scale. Here, we report the results of a large XMM-Newton campaign in 2015 to study these short delays further. Analyzing high quality data that span time scales between hours and decades, we find that neutral and ionized absorption contribute significantly to the spectral shape. Accounting for their effects, we find no evidence for a relativistic reflection component, contrary to early work. Energy-dependent lags are significantly measured in the new data, but with an energy profile that does not resemble a broad iron line, in contrast to the old data. The complex lag-energy spectra, along with the lack of strong evidence for a relativistic spectral component, suggest that the energy-dependent lags are produced by absorption effects. The long term spectral variations provide new details on the variability of the narrow Fe K$alpha$ line . We find that its variations are correlated with, and delayed with respect to, the primary X-ray continuum. We measure a delay of $tau= 3.3^{+1.8}_{-0.7}$ days, implying an origin in the inner broad line region (BLR). The delay is half the H$beta$ line delay, suggesting a geometry that differs slightly from the optical BLR.
We present X-ray spectral analysis of Seyfert 1.5 Active Galactic Nuclei (AGN) NGC~4151 using textit{NuSTAR} observation during 2012. This is the first attempt to fit an AGN data using the physical Two Component Advective flow (TCAF) solution. We dis
NGC 4151 is among the most well-studied Seyfert galaxies that does not suffer from strong obscuration along the observers line-of-sight. This allows to probe the central active galactic nucleus (AGN) engine with photometry, spectroscopy, reverberatio
We discuss the spectral and timing properties of the accreting millisecond X-ray pulsar SWIFT J1756.9-2508 observed by XMM-Newton, NICER and NuSTAR during the X-ray outburst occurred in April 2018. The spectral properties of the source are consistent
We report on the spectral and timing properties of the accreting millisecond X-ray pulsar IGR J00291+5934 observed by XMM-Newton and NuSTAR during its 2015 outburst. The source is in a hard state dominated at high energies by a comptonization of soft
IGR J17511-3057 is the second X-ray transient accreting millisecond pulsar discovered by INTEGRAL. It was in outburst for about a month from September 13, 2009. The broad-band average spectrum is well described by thermal Comptonization with an elect