Time-dependent photoionisation modelling of AGN outflows

Over the last four decades several photoionisation codes have been developed. Based on a high degree of complexity in terms of physical processes considered in the modelling, they achieve robust predictions. Nevertheless, the temporal dependencies of the ionisation balance equations are often neglected in favour of a scenario in which the plasma is constantly in photoionisation equilibrium with the ionising radiation. Here we present a new self-consistent photoionisation model where ionisation balance, energy and temperature are considered in their full time-dependent form. This time-dependent photoionisation model (TPHO) is particularly applicable to AGN outflows where the ionisation source, the UV and X-ray continuum, is highly variable. In particular, the synergy between TPHO and time-resolved X-ray spectroscopy studies enables us to monitor the response of the plasma in outflow to variations in the illuminating continuum. The estimated recombination timescales depends on the electron density. Thus, TPHO not only characterises the non-equilibrium AGN absorbers (e.g. warm absorbers), but also infers their density and spatial distance from the central source. Mapping the outflows will ultimately help to reveal the energetics of the AGN outflows and quantify their impact on the surrounding environment; a phenomenon usually termed AGN feedback.