Variability and the size-luminosity relation of the intermediate mass
  AGN in NGC 4395
  We present the variability study of the lowest-luminosity Seyfert 1 galaxy
NGC 4395 based on the photometric monitoring campaigns in 2017 and 2018. Using
22 ground-based and space telescopes, we monitored NGC 4395 with a $\sim$5
minute cadence during a period of 10 days and obtained light curves in the UV,
V, J, H, and K/Ks bands as well as the H$\alpha$ narrow-band. The RMS
variability is $\sim$0.13 mag on \emph{Swift}-UVM2 and V filter light curves,
decreasing down to $\sim$0.01 mag on K filter. After correcting for continuum
contribution to the H$\alpha$ narrow-band, we measured the time lag of the
H$\alpha$ emission line with respect to the V-band continuum as
${55}^{+27}_{-31}$ to ${122}^{+33}_{-67}$ min. in 2017 and ${49}^{+15}_{-14}$
to ${83}^{+13}_{-14}$ min. in 2018, depending on the assumption on the
continuum variability amplitude in the H$\alpha$ narrow-band. We obtained no
reliable measurements for the continuum-to-continuum lag between UV and V bands
and among near-IR bands, due to the large flux uncertainty of UV observations
and the limited time baseline. We determined the AGN monochromatic luminosity
at 5100\AA\ $\lambda L_\lambda = \left(5.75\pm0.40\right)\times
10^{39}\,\mathrm{erg\,s^{-1}}$, after subtracting the contribution of the
nuclear star cluster. While the optical luminosity of NGC 4395 is two orders of
magnitude lower than that of other reverberation-mapped AGNs, NGC 4395 follows
the size-luminosity relation, albeit with an offset of 0.48 dex
($\geq$2.5$\sigma$) from the previous best-fit relation of Bentz et al. (2013).
