Time-Dependent AGN Disc Winds I -- X-ray Irradiation

We study AGN line driven disc winds using time-dependent radiation hydrodynamics. The key criterion for determining wind launching is the coupling strength of the UV radiation field via the spectral lines of the gas. The strength of these lines in turn relies crucially on the gas ionization state, determined by the local X-ray intensity. We consider a suite of models where the central ionizing radiation is affected by scattering, absorption and re-emission by the intervening gas. In a pure attenuation model, the disc launches an episodic wind, as previous studies have shown. Including scattering or re-emission tends to weaken the wind, lowering the mass flux and outflow velocity and if sufficiently dominant, suppressing the outflow entirely. However, the exponential nature of radiative attenuation means only a modest, factor of a few, increase in the absorption cross section can overcome the wind suppression due to scattering and re-emission. We find mass outflow rates of $\sim 20\%$ or more of the assumed inflow rate through the disk, indicating that radiation driven winds may significantly alter the structure of the accretion flow. The winds also supply a large, time-varying column of material above the nominal constant disk scale height, which will determine the geometry of reprocessed emission from the central source. Our results suggest the need for accurate photoionization modeling, radiation transport as well as accretion disc physics, to study their effects on the AGN disc winds