NICER observation list: Target ID 469301

The soft excess is smooth spectral component that is observed ubiquitously in AGN. Its origin is not clear. Recent modeling suggests that relativistic reflection or Comptonization in warm corona both explain its spectral shape. We propose to monitor two sources PG 1404+226 and TON S180 to track how the soft excess varies relative to the primary power on time scales comparable to the viscous time scale at the inner accretion disk. The two sources have comparable masses, but very different strengths for the soft excess. Obtaining characteristic variability time scale and comparing how observable such the photon index and flux in different bands vary with time, will allow the models to be tested.