Modelling photometric reverberation data: a disk-like broad-line region and a potentially larger black hole mass for 3C 120

Abstract

We consider photometric reverberation mapping, where the nuclear continuum variations are monitored via a broad-band filter and the echo of emission line clouds of the broad-line region (BLR) is measured with a suitable narrow-band (NB) filter. We investigate how an incomplete emission-line coverage by the NB filter influences the determination of the BLR size. This includes two basic cases: 1) a symmetric cut of the blue and red part of the line wings; and 2) the filter positioned asymmetrically to the line centre so that essentially a complete half of the emission line is contained in the NB filter. Under the assumption that the BLR is dominated by circular Keplerian orbits, we find that symmetric cutting of line wings may lead to overestimating the BLR size by less than 5%. The case of asymmetric half-line coverage, similar as for our data of the Seyfert 1 galaxy 3C 120, yields a BLR size with a bias of less than 1%. Our results suggest that any BLR size bias due to a narrow-band line cut in photometric reverberation mapping is small and in most cases negligible. We used well-sampled photometric reverberation mapping light curves with sharp variation features in both the continuum and the Hβ light curves to determine the geometry type of the Hβ BLR for 3C 120. Modelling of the light curve, under the assumption that the BLR is essentially virialised, argues against a spherical geometry and favours a nearly face-on disk-like geometry with an inclination i = 10 • ± 4 • and an extension from 22 to 28 light days. The low inclination may lead to a larger black hole mass M BH than that derived when using the average geometry scaling factor f = 5.5. We discuss deviations of Seyfert 1 galaxies from the M BH -σ * relation.

Application of the spine-layer jet radiation model to outbursts in the broad-line radio galaxy 3C 120

“…Pozo Nuñez et al (2014) calculated the location of the thin-disk BLR in 3C 120 between 22 and 28 light days (l.d.) from the central BH with reverberation mapping technique.…”

Revisiting correlations between broad-line and jet emission variations for AGNs: 3C 120 and 3C 273

“…Kollatschny et al 2014;Pozo Nuñez et al 2014). The disk-like BLR has a ratio of height to radius C = H/r.…”

“…The disk-like BLR geometry of 3C 120 has been established in Kollatschny et al (2014) and Pozo Nuñez et al (2014). Then Rjet will be re-calculated on the basis of equation (19).…”

“…• and an extension from 22 to 28 light-days (Pozo Nuñez et al 2014). If the viewing angle α = 10 ± 4…”

“…Recently, Kollatschny et al (2014) and Pozo Nuñez et al (2014) derived larger masses of the order of 10 8 M⊙ for 3C 120. 3C 120 has Rjet =1.1-1.5 pc and a mass of the order of 10 8 M⊙.…”