Determination of the size of the dust torus in H0507+164 through optical and infrared monitoring

Abstract

The time delay between flux variations in different wavelength bands can be used to probe the inner regions of active galactic nuclei (AGN). Here, we present the first measurements of the time delay between optical and near-infrared (NIR) flux variations in H0507+164, a nearby Seyfert 1.5 galaxy at z = 0.018. The observations in the optical V-band and NIR J, H and K s bands carried over 35 epochs during the period October 2016 to April 2017 were used to estimate the inner radius of the dusty torus. From a careful reduction and analysis of the data using crosscorrelation techniques, we found delayed responses of the J, H and K s light curves to the V-band light curve. In the rest frame of the source, the lags between optical and NIR bands are found to be 27.1 +13.5 −12.0 days (V vs. J), 30.4 +13.9 −12.0 days (V vs. H) and 34.6 +12.1 −9.6 days (V vs. K s). The lags between the optical and different NIR bands are thus consistent with each other. The measured lags indicate that the inner edge of dust torus is located at a distance of 0.029 pc from the central UV/optical AGN continuum. This is larger than the radius of the broad line region of this object determined from spectroscopic monitoring observations thereby supporting the unification model of AGN. The location of H0507+164 in the τ-M V plane indicates that our results are in excellent agreement with the now known lag-luminosity scaling relationship for dust in AGN.

Rapid luminosity decline and subsequent reformation of the innermost dust distribution in the changing-look AGN Mrk 590

“…As for the variable component, the V -band light curve of Mrk 590 is dominated by disk continuum emission, and the K-band light curve is dominated by hot dust emission from the dust torus. However, the K-band flux may include a flux contribution from the long wavelength tail of the disk continuum emission (Minezaki et al 2006;Tomita et al 2006;Kishimoto et al 2008;Koshida et al 2014;Mandal et al 2018). Although the minor contribution of the disk continuum emission in the K band is ignored in the CCF analysis here, the obtained dust lags are consistent with τ rest, dust = 36.2 +2.6 −2.6 day reported by Koshida et al (2014), in which the disk continuum emission was subtracted by extrapolating the V -band light curve assuming a power-law continuum of αν = 0.…”

“…The BLR reverberation mapping observations for local Seyfert galaxies and some high redshift quasars have been carried out by several groups (e.g., Peterson et al 1998Peterson et al , 2004Kaspi et al 2000;Bentz et al 2009b;Denney et al 2010;Grier et al 2012;Du et al 2014;Fausnaugh et al 2017); a compilation of ∼ 40 AGNs with secure Hβ BLR lag detection can be found in Bentz & Katz (2015) (see also Bentz et al 2009aBentz et al , 2013. Dust reverberation mapping observations have also been measured for several AGNs (Clavel et al 1989;Glass 1992;Sitko et al 1993;Glass 2004;Suganuma et al 2006;Koshida et al 2014;Pozo Nuñez et al 2014Schnülle et al 2015;Lira et al 2015;Vazquez et al 2015;Mandal et al 2018;Ramolla et al 2018;Landt et al 2019). The first systematic investigation of dust reverberation mapping was carried out by the Multicolour Active Galactic Nuclei Monitoring (MAGNUM) project (Yoshii 2002;Yoshii et al 2003;Minezaki et al 2004;Tomita et al 2006;Suganuma et al 2006;Koshida et al 2009;Sakata et al 2010;Koshida et al 2014;Yoshii et al 2014).…”

A status report on AGN variability

“…Hence, the K-band corresponds to the near-infrared wavelength where the torus emission dominates, while the J and H bands might still show a strong disk contribution. Cross-correlation between K-band light curves and those obtained in the optical show that the torus follows the variations seen in the accretion disk but with a lag corresponding to the light travel time to the sublimation radius (Clavel et al 1989;Suganuma et al 2006;Koshida et al 2014;Lira et al 2011Lira et al , 2015Pozo et al 2014Pozo et al , 2015Mandal et al 2018). The lags observed in local Seyfert galaxies are in the 40-400 day range, corresponding to distances of fractions of a pc to a few pc.…”

Modeling the Infrared Reverberation Response of the Circumnuclear Dusty Torus in AGNs: An Investigation of Torus Response Functions

“…It has also been suggested that a component of hot graphite dust residing within the ISM dust sublimation radius is required to account for a peak in the NIR SED of broad-line AGN (Mor & Netzer 2012; 10 42 10 43 10 44 10 2 10 1 10 0 r lag (pc) Rd,ISM,iso Rd,C,iso toriso 10 42 10 43 10 44 10 45 10 2 10 1 10 0 toraniso Suganuma et al 2006Clavel et al 1989Koshida et al 2014Pozo Nunez et al 2015& 2014Mandal et al 2018Lira et al 2011& 2015 L V (erg/s) Fig. 23.-The K-band radius-luminosity relationships for the observationally determined values of r K available in the literature (Clavel et al 1989;Suganuma et al 2006;Lira et al 2011;Koshida et al 2014;Pozo Nuñez et al 2014;Lira et al 2015;Pozo Nuñez et al 2015;Mandal et al 2018) and for r RW,K values derived from a subset of our globally optically thick torus models. The values of r RW corresponding to the median value of the RWD and the range between minimum and maximum RWD values at λ = 2.2 µm are represented by a solid line and a shaded band, respectively, for both the isotropically (blue; left panel) and anisotropically (red; right panel) illuminated torus.…”

“…The dust reverberation radius has now been measured by NIR (K-band) reverberation mapping for about 20 AGN (e.g., Nelson 1996;Oknyanskij & Horne 2001;Minezaki et al 2004;Suganuma et al 2006;Lira et al 2011;Koshida et al 2014;Pozo Nuñez et al 2014;Lira et al 2015;Mandal et al 2018). Some of the authors of this paper are members of a collaboration that recently conducted a 2.5 year monitoring campaign, during which 12 broad-line AGN were observed using the Spitzer Space Telescope at 3.6 and 4.5 µm, supported by ground-based optical observations.…”