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Description
We present a variability study of the lowest-luminosity Seyfert 1 nucleus of the galaxy NGC 4395 based on photometric monitoring campaigns in 2017 and 2018. Using 22 ground-based and space telescopes, we monitored NGC 4395 with a ~5-minute cadence during a period of 10 days and obtained light curves in the ultraviolet (UV), V, J, H, and K/K_s_ bands, as well as narrowband H{alpha}. The rms variability is ~0.13mag in the Swift UVM2 and V filter light curves, decreasing down to ~0.01mag in the K filter. After correcting for the 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_-31_^+27^-122_-67_^+33^min in 2017 and 49_-14_^+15^-83_-14_^+13^min in 2018, depending on assumptions about 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, owing to the large flux uncertainty of UV observations and the limited time baseline. We determined the active galactic nucleus (AGN) monochromatic luminosity at 5100{AA}, {lambda}L_{lambda}_=(5.75+/-0.40)x10^39^erg/s, 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 0.48dex (>=2.5{sigma}) from the previous best-fit relation of Bentz+ 2013ApJ...767..149B
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