Variability and the Size–Luminosity Relation of the Intermediate-mass AGN in NGC 4395

Abstract

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/Ks bands as well as narrow-band Hα. The rootmean-square (RMS) variability is ∼ 0.13 mag in the Swift-UVM2 and V filter light curves, decreasing down to ∼ 0.01 mag in the K filter. After correcting for the continuum contribution to the Hα narrowband, we measured the time lag of the Hα 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 Hα 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 5100Å, λL λ = (5.75 ± 0.40) × 10 39 erg s −1 , after 2 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 (≥ 2.5σ) from the previous best-fit relation of Bentz et al. (2013).

Investigation of active galactic nuclei in time domain era

“…This was used in case of NGC 4395, which is a bulgeless dwarf galaxy with one of the smallest SMBH of only 10,000 solar masses (Woo et al 2019). This SMBH mass was confirmed with the international intranight RM campaign done by more than a dozen of telescope across the world including the 1.4m Milankovic telescope (Cho et al 2020). The observed time delays of the BLR were only ∼1-2 hours, and it was important to show that this case of very low-luminosity AGN follows the radius-luminosity scaling relations (Bentz et al 2013).…”

Caucasian mountain observatory of Sternberg astronomical institute: six years of operation

“…-Variability and size-luminosity relation of AGNs (Oknyansky et al 2017;Ilić et al 2020;Cho et al 2020) -Study of variable stars associated with maser sources (Sobolev et al 2019) -Star-forming regions at the periphery of the supershell surrounding the Cyg OB1 association (Sitnik et al 2020(Sitnik et al , 2019Tatarnikova et al 2016) -Optical and NIR-photometry of X-ray sources with black holes, microquasars, pre-main sequence and post-AGB objects (Cherepashchuk et al 2019a,b) -Spectroscopy of an ultramassive white dwarf (Pshirkov et al 2020) -Colour and polarimetric variability of UXORs; young stellar object jets photometry (Dodin et al 2020a(Dodin et al , 2019Berdnikov et al 2017) -Analysis of temporal evolution of the circumstellar envelopes of evolved stars at high angular resolution (Safonov et al 2019b;Fedoteva et al 2020) -Spectral characterization of solar system bodies (Busarev et al 2018) -Near-infrared photometry of superthin edge-on galaxies (Bizyaev et al 2020) -Spectral characterization and identification of SRG/eRosita sources (Dodin et al 2020b) -High-accuracy monitoring of exoplanet transits (Benni et al 2020).…”

Refining the mass estimate for the intermediate-mass black hole candidate in NGC 3319

“…den Brok et al (2015) obtained a black hole mass estimate of 4.0 +2.7 −1.0 × 10 5 M via gas dynamical modelling; Brum et al (2019) similarly obtained 2.5 +1.0 −0.8 × 10 5 M via gas kinematics. These direct measurements were preceded by informative RM black hole mass estimates of (3.6±1.1)× 10 5 M (Peterson et al, 2005) and (4.9 ± 2.6) × 10 4 M (Edri et al, 2012, see also Cho et al 2020 andBurke et al 2020). Likewise, NGC 3319* could greatly benefit from further study by RM campaigns, or at least single-epoch spectra mass estimates.…”