During the 2014 HST/Swift and ground-based multi-wavelength monitoring campaign of NGC 5548 (AGN STORM), the UV-optical broad emission lines exhibited anomalous, decorrelated behaviour relative to the far-UV continuum flux variability. Here, we use key diagnostic emission lines (Ly-alpha and He II) for this campaign to infer a proxy for the all important, variable driving EUV continuum incident upon BLR clouds. The inferred driving continuum provides a crucial step towards the recovery of the broad emission line response functions in this AGN. In particular, the ionising continuum seen by the BLR was weaker and softer during the anomalous period than during the first third of the campaign, and apparently less variable than exhibited by the far-UV continuum. We also report the first evidence for anomalous behaviour in the longer wavelength (relative to 1157A) continuum bands. This is corroborative evidence that a significant contribution to the variable UV-optical continuum emission arises from a diffuse continuum emanating from the same gas that emits the broad emission lines.
@article{arxiv.1904.12588,
title = {Anomalous behaviour of the UV-optical continuum bands in NGC 5548},
author = {M. R. Goad and C. Knigge and K. T. Korista and E. Cackett and K. Horne and D. A. Starkey and B. M. Peterson and G. De Rosa and G. A. Kriss and R. Edelson and M. Fausnaugh},
journal= {arXiv preprint arXiv:1904.12588},
year = {2019}
}
Comments
17 pages, 8 figures, accepted for publication in MNRAS 2019 April 25