Swift/UVOT grism monitoring of NGC 5548 in 2013: an attempt at MgII
  reverberation mapping
  Reverberation-mapping-based scaling relations are often used to estimate the
masses of black holes from single-epoch spectra of AGN. While the
radius-luminosity relation that is the basis of these scaling relations is
determined using reverberation mapping of the H$\beta$ line in nearby AGN, the
scaling relations are often extended to use other broad emission lines, such as
MgII, in order to get black hole masses at higher redshifts when H$\beta$ is
redshifted out of the optical waveband. However, there is no radius-luminosity
relation determined directly from MgII. Here, we present an attempt to perform
reverberation mapping using MgII in the well-studied nearby Seyfert 1, NGC
5548. We used Swift to obtain UV grism spectra of NGC 5548 once every two days
from April to September 2013. Concurrent photometric UV monitoring with Swift
provides a well determined continuum lightcurve that shows strong variability.
The MgII emission line, however, is not strongly correlated with the continuum
variability, and there is no significant lag between the two. We discuss these
results in the context of using MgII scaling relations to estimate
high-redshift black hole masses.
