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arXiv · 1502.07502

The largest Swift AGN monitoring campaign: UV/optical variability in NGC 5548

S. D. Connolly·I. M. McHardy·D. T. Cameron·T. Dwelly·P. Lira·D. Emmanoulopoulos·J. Gelbord·E. Breedt·P. Arevalo·P. Uttley
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Abstract

We report on the largest Swift AGN monitoring program, concerning UV/optical variability in Seyferts. From 554 observations, over a 750d period, of the Seyfert galaxy NGC 5548, we see (McHardy et al. 2014) a good overall correlation between the X-ray and UV/optical bands,particularly on short timescales (tens of days). The UVOT bands are found to lag behind X-rays with a lag scaling as wavelength to the power 1.23 +/- 0.31, in excellent agreement with that expected (1.33) if UV/optical variability arises from reprocessing of X-rays by the accretion disc. However, the observed lags are ~3 times longer than expected from a standard Shakura-Sunyaev disc, raising real concerns about the detailed validity of this model. The results can be explained with a slightly larger mass and accretion rate, and a hotter disc, or if the disc is clumpy, thereby enhancing the emission from the outer regions.

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S. D. Connolly, I. M. McHardy, D. T. Cameron, T. Dwelly, P. Lira, D. Emmanoulopoulos, J. Gelbord, E. Breedt, P. Arevalo, P. Uttley. 2015-02-26. The largest Swift AGN monitoring campaign: UV/optical variability in NGC 5548. https://arxiv.org/abs/1502.07502

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