Characterizing X-ray, UV, and optical variability in NGC 6814 using high-cadence Swift observations from a 2022 monitoring campaign(vol 531 , pg 3729 , 2024)

We present the first results of a high-cadence Swift monitoring campaign (3-4 visits per day for 75 d) of the type 1.5 Seyfert galaxy NGC 6814 characterizing its variability throughout the X-ray and ultraviolet (UV)/optical wavebands. Structure function analysis reveals an X-ray power law (alpha = 0.5(-0.1)(+0.2)) that is significantly flatter than the one measured in the UV/optical bands (<alpha > approximate to 1.5), suggesting different physical mechanisms driving the observed variability in each emission region. The structure function break-time is consistent across the UV/optical bands (<tau > approximate to 2.3 d), suggesting a very compact emission region in the disc. Correlated short time-scale variability measured through cross-correlation analysis finds a lag-wavelength spectrum that is inconsistent with a standard disc reprocessing scenario (tau alpha lambda(4/3)) due to significant flattening in the optical wavebands. Flux-flux analysis finds an extremely blue active galactic nucleus (AGN) spectral component (F-nu proportional to lambda(-0.85)) that does not follow a standard accretion disc profile (F nu proportional to lambda(-1/3)). While extreme outer disc truncation (R-out = 202 +/- 5 r g) at a standard accretion rate ((m) over dot(Edd) = 0.0255 +/- 0.0006) may explain the shape of the AGN spectral component, the lag-wavelength spectrum requires more modest truncation (R-out = 1382(-404)(+398)r(g)) at an extreme accretion rate ((m) over dot(Edd) = 1.3(-0.9)(+2.1)). No combination of parameters can simultaneously explain both results in a self-consistent way. Our results point towards the possibility of a non-standard disc geometry in NGC 6814.