Date: Monday 06-Jun-2016
Time: 11:00-12:00
Location: PSC 1148
Speaker: Catia de Jesus Silva (University of Amsterdam)
Title: "Spectral-timing analysis of warm absorbers in AGN - The case study of NGC 4051"
AGN feedback may play an important role in galaxy and cluster evolution. In the case of Seyfert I galaxies, outflows are highly ionized and remarkably complex in their structure. While the observed spectra provides information on the column density and outflowing velocities of the gas, determining its radial location, and thus its impact on the surrounding environment, is not trivial. Monitoring the response of the gas to the variability of the ionizing continuum, results in an estimation of a response time, from which the density of the gas, and hence its distance, can be determined. We have performed a detailed analysis through a time-dependent photoionization code in combination with spectral and Fourier spectral-timing techniques, to study in detail the response of the gas due to variations in the ionizing luminosity. Our results suggest that the observed X-ray time lags may carry a signature of the warm absorber response time to changes in the ionizing continuum (Silva, Uttley & Costantini 2016, submitted to A&A). X-ray time lags of AGN often show a characteristic behaviour, displaying a hard lag at low Fourier frequencies and a soft lag at high Fourier frequencies. The soft lag has been explained through reverberation from reflected emission, and it has been suggested that propagation of fluctuations in the accretion flow may explain the hard lag. We have found that the warm absorber alone, in NGC 4041, is capable of producing a soft lag (~100s), on timescales of ~ hours. This will have implications for the modelling of the hard lags, observed on the same timescales. In this talk, I will show that using spectral-timing analysis together with a time-dependent photoionization model is an extremely powerful method, not only to assess the contribution of the warm absorber to the X-ray time lags of AGN, but also having the potential to provide important diagnostics on the warm absorber location and gas density. In particular, our method is extremely promising for future missions, when higher signal to noise grating or calorimeter data become available.
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