tokens: than those within the UV/optical, and Figure 3 (top) indicates a diversity of X-ray/optical lags, with the X-rays leading the UV in three cases and lagging in the fourth. This poses a severe problem for the reprocessing model, for which no simple solution is currently apparent. Swift is the workhorse without which IDRM cannot (currently) be successfully performed on AGN, as it is the only fully operational observatory that provides coverage throughout the X-ray, UV, and optical regimes necessary for this experiment. However, it is also very helpful to expand coverage to longer wavelengths and higher spectral resolution than that afforded by the UVOT alone. We note that simultaneous ground-based optical monitoring has been performed on all four of these targets, and the first data set (on NGC 5548) has already been published (Fausnaugh et al. 2016 ). Reduction and analysis of optical photometry and spectroscopy on the other three is ongoing and will be published shortly. This should provide further constraints on the accretion disk fits (especially the overall size) and possibly on the effects of line and diffuse emission from the BLR. Note as well that HST can also play a crucial role, providing much higher spectral resolution that can allow direct detection and modeling of the BLR continuum component, and extending the UV coverage to wavelengths as short as ∼1150 Å. That has been used to resolve the excess lag around the Balmer jump in one of these targets (NGC 4593, Cackett et al. 2018 ), and it is expected to play a prominent role in future campaigns. These unprecedented data also reveal the need for improvements in our time-series analysis tools. The uncertainties on lags output by JAVELIN (Zu et al. 2011 ) are on average a factor of ∼2.5 smaller than the same quantity output by the ICCF FR/RSS technique (Peterson et al. 1998 ). The precise cause of this discrepancy has not been determined, but given the fact that the older ICCF FR/RSS technique is more conservative in its assumptions and results, it and not JAVELIN was utilized to derive the results reported above. More generally, there is no interband lag tool currently in use that allows separation of two distinct interband lag signals, as seems to be the case in the UV/optical, where short lags from the accretion disk and longer lags from the BLR appear to be present. Ultimately these techniques will need to be developed and directly compared so as to determine which are more reliable and suitable for studying AGN interband lags, but that is beyond the the scope of the current paper. These results also highlight the need for theoretical progress, especially in understanding the X-ray emission component(s) and relation to the disk and BLR that emit at lower energies. These observations present severe problems for the “lamp-post” reprocessing model. Can it be modified or must it be discarded? If it is the latter then what will take its place? The current set of reduced data are
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