Eleven years of monitoring the Seyfert 1 Mrk 335 with Swift: Characterizing the X-ray and UV/optical variability

The narrow-line Seyfert 1 galaxy (NLS1) Mrk 335 has been continuously monitored with Swift since May 2007 when it fell into a long-lasting, X-ray low-flux interval. Results from nearly 11 years of monitoring are presented here. Structure functions are used to measure the UV-optical and the X-ray power spectra. The X-ray structure function measured between 10 and 100 d is consistent with the flat, low-frequency part of the power spectrum measured previously in Mrk 335. The UV-optical structure functions of Mrk 335 are comparable with those of other Seyfert 1 galaxies and of Mrk 335 itself when it was in a normal bright state. There is no indication that the current X-ray low-flux state is attributed to changes in the accretion disc structure of Mrk 335. The characteristic time-scales measured in the structure functions can be attributed to the thermal (for the UV) and the dynamic (for the optical) time-scales in a standard accretion disc. The high-quality UVW2 (∼1800 Å in the source frame) structure function appears to have two breaks and two different slopes between 10 and 160 d. Correlations between the X-ray and other bands are not highly significant when considering the entire 11-yrlight curves, but more significant behaviour is present when considering segments of the light curves. A correlation between the X-ray and the UVW2 in 2014 (Year-8) may be predominately caused by a giant X-ray flare that was interpreted as a jet-like emission. In 2008 (Year-2), possible lags between the UVW2 emission and other UV-optical waveband may be consistent with reprocessing of X-ray or UV emission in the accretion disc.