AGN STORM 2. IV. Swift XRT and UVOT monitoring

As part of this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15 months, obtaining observations in X-rays and six UV/optical filters. The X-ray monitoring shows that Mrk 817 was in a significantly fainter state than in previous observations, with only a brief flare where it reached prior flux levels.

The X-ray spectrum is heavily obscured. The UV/optical light curves show significant variability throughout the campaign and are well correlated with one another, but uncorrelated with the X-rays. Combining the Swift UV/optical light curves with Hubble Space Telescope UV continuum light curves, we measure interband continuum lags, {tau}({lambda}), that increase with increasing wavelength roughly following {tau}({lambda}){\prop}{lambda}^4/3^, the dependence expected for a geometrically thin, optically thick, centrally illuminated disk.