Unveiling broad line region structure in active galactic nuclei with high resolution X-ray spectra. An analytic approach to wind emission line profiles

has provided an unprecedented view of the emission and absorption lines in the X-ray. Notably, early results showed significant complexity to the Fe-Kα line profile in active galactic nuclei (AGN), with clear contributions from at least three emitting structures: an inner disc, intermediary broad line region (BLR) scale material, and an outer torus. This poses a new challenge for the modelling of the emission lines as, while fast sophisticated models for disc line-profiles exist, large scale-height material is typically much more complex. In this paper we aim to address this gap, by building a fully analytic model for the emission line profiles from a wind, aimed towards BLR scale material, motivated on previous reverberation studies suggesting a wind on the inner edge of the BLR. Our approach gives a physically motivated, yet computationally fast, model for the intermediary component to the Fe-Kα complex seen in the data. We demonstrate our model on the observations of NGC,4151 from the performance verification phase, showing that it gives a good description of the data, with physically reasonable parameters for BLR scale material. We also show that our model naturally gives the `smooth' line profile seen in the data, due to the large spatial extent of a wind. Finally, we make our model code public to the community, and name it xwind .