Tracking The Long Term Variability of the Soft Excess in NLS1

A puzzling feature the X-ray spectra of AGN is the so-called soft excess. This is a strong excess of emission that is observed above the extrapolation of the power-law from the hot corona to energies below 1 keV. Several models have been proposed to explain its origin, each having its strengths and weaknesses. In this work, we use NICER monitoring programs to track how the soft excess emission vary on weeks to months time scales in sources showing different excess strengths. Our goal is to search for a characteristic variability time scale of the soft excess relative to the central corona, and track how the spectra change with time and compare that to different model predictions. We find evidence that the soft excess emission regions is co-spacial with corona, challenging models where the two are emitted from different regions. Tracking the changes in the spectral shape provides constraint on the optical depth and heating rates for the gas producing the soft excess.