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 \sim 5 minute cadence during a period of 10 days and obtained light curves in the ultraviolet ( UV ) , V , J , H , and K / Ks bands as well as narrow-band H \alpha .
The root-mean-square ( RMS ) variability is \sim 0.13 mag in the Swift - UVM2 and V filter light curves , decreasing down to \sim 0.01 mag 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 } ^ { +27 } _ { -31 } to { 122 } ^ { +33 } _ { -67 } min in 2017 and { 49 } ^ { +15 } _ { -14 } to { 83 } ^ { +13 } _ { -14 } 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 Å , \lambda L _ { \lambda } = \left ( 5.75 \pm 0.40 \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 .