2018ApJ...863..178M

We present the first results from a detailed analysis of a new, long (∼100 ks) XMM-Newton observation of the narrow-line Seyfert 1 galaxy PG 1404+226, which showed a large-amplitude, rapid X-ray variability by a factor of ∼7 in ∼10 ks with an exponential rise and a sharp fall in the count rate. We investigate the origin of the soft X-ray excess emission and rapid X-ray variability in the source through time-resolved spectroscopy and fractional rms spectral modeling. The strong soft X-ray excess below 1 keV observed in both the time-averaged and time-resolved spectra is described by the intrinsic disk Comptonization model as well as the relativistic reflection model where the emission is intense merely in the inner regions (r_in< 1.7r_g) of an ionized accretion disk. We detected no significant UV variability, while the soft X-ray excess flux varies together with the primary power-law emission (as F_primary∝F_excess^1.54), although with a smaller amplitude, as expected in the reflection scenario. The observed X-ray fractional rms spectrum is approximately constant with a drop at ∼0.6 keV and is described by a non-variable emission line component with the observed energy of ∼0.6 keV and two variable spectral components: a more variable primary power-law emission and a less variable soft excess emission. Our results suggest the "lamppost geometry" for the primary X-ray-emitting hot corona, which illuminates the innermost accretion disk due to strong gravity and gives rise to the soft X-ray excess emission.