The response of warm absorbers to the variations in the ionizing continuum in the active galaxy NGC4051

Abstract

We investigate the response of warm absorbers to variations in the ionizing continuum of the Seyfert 1 galaxy NGC 4051 using time-resolved X-ray observations from the Neutron Star Interior Composition Explorer (NICER). In this work, we have demonstrated we can perform time-resolved spectroscopic studies of warm absorbers of about ∼ 5500 s time resolution using NICER data. We have extracted 15 spectra for this source, corresponding to 15 different visits to the source, or pointings, each separated by a longer Earth occultation. By modeling the spectral variability of the warm absorber with the warmabs analytic model, we detect significant variations in the ionization parameter that correlate with changes in the ionizing flux. A time lag of approximately 5500 seconds is observed between the flux variations and the absorber's ionization response, suggesting that the gas is out of photoionization equilibrium during these periods. Using this time lag, we estimate the lower limit of the gas density 8.91 × 10⁶cm⁻³ and constrain the location of the warm absorber to within 7.02 × 10¹⁶ cm (∼ 0.02 parsec) from the central black hole. This study uses time-resolved spectral analysis to contribute to our understanding of the physical conditions of ionized AGN outflows, such as density and location.