Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XI. Accretion Disk Reverberation Mapping of Mrk 142

Abstract

We performed an intensive accretion disk reverberation mapping campaign on the high accretion rate active galactic nucleus Mrk 142 in early 2019. Mrk 142 was monitored with the Neil Gehrels Swift Observatory for four months in X-rays and six different UV/optical filters. Ground-based photometric monitoring was obtained from the Las Cumbres Observatory, the Liverpool Telescope, and the Dan Zowada Memorial Observatory in ugriz filters, as well as from the Yunnan Astronomical Observatory in V. Mrk 142 was highly variable throughout, displaying correlated variability across all wavelengths. We measure significant time lags between the different wavelength lightcurves. In the UV and optical, we find that the wavelength-dependent lags, τ(λ), generally follow the relation τ(λ) ∝ λ 4/3, as expected for the T ∝ R −3/4 profile of a steady-state, optically thick, geometrically thin accretion disk, though they can also be fit by τ(λ) ∝ λ 2, as expected for a slim disk. The exceptions are the u and U bands, where an excess lag is observed, as has been observed in other active galactic nuclei and attributed to continuum emission arising in the broad-line region. Furthermore, we perform a flux–flux analysis to separate the constant and variable components of the spectral energy distribution, finding that the flux dependence of the variable component is consistent with the f ν ∝ ν 1/3 spectrum expected for a geometrically thin accretion disk. Moreover, the X-ray to UV lag is significantly offset from an extrapolation of the UV/optical trend, with the X-rays showing a poorer correlation with the UV than the UV does with the optical. The magnitude of the UV/optical lags is consistent with a highly super-Eddington accretion rate.

Possible mechanism for multiple changing-look phenomena in active galactic nuclei

“…The second equally important aspect is the time delay in the signal propagation. The current model assumes that the change in the irradiation patters happens without any time delay, while actually the outer parts of the disk react with significant time delay of days, as is well known from reverberation studies of AGN continua (e.g., Collier et al 1998;Sergeev et al 2005;Cackett et al 2007Cackett et al , 2020Edelson et al 2015, and the references therein). The response of the emission lines is delayed even more strongly as shown by numerous campaigns (e.g., Liutyi 1977;Collier et al 1998;Kaspi et al 2000;Peterson et al 2004;Grier et al 2017;Du et al 2018), thus the final model has to include these effects, particularly in the case of relatively fast variations in the source.…”

Reverberation mapping of active galactic nuclei: From X-ray corona to dusty torus

“…Figure 6 shows some examples of these recent results.

Figure 6 Wavelength-dependent continuum lags in NGC 5548 ( Fausnaugh et al., 2016 ), NGC 4593 ( Cackett et al., 2018 ), and Mrk 142 ( Cackett et al., 2020 ) Data from Swift (black circles), HST (red squares), and ground-based observatories (blue triangles). The solid lines show the best-fitting relation (excluding the X-rays and bands), while the dashed lines show the predicted lags based on reasonable estimates of the black hole mass and accretion rate (Equation 12 in Fausnaugh et al., 2016 )).

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“… Wavelength-dependent continuum lags in NGC 5548 ( Fausnaugh et al., 2016 ), NGC 4593 ( Cackett et al., 2018 ), and Mrk 142 ( Cackett et al., 2020 ) …”

“…Recent studies (e.g. McHardy et al., 2018 ; Cackett et al., 2020 ; Hernández Santisteban et al., 2020 ) that perform a flux-flux analysis to calculate the variable spectrum show that the bands are also enhanced there (e.g. approximately 15% in Mrk 142), but overall the variable spectrum follows a simple power law.…”

The Sloan Digital Sky Survey Reverberation Mapping Project: Photometric g and i Light Curves

“…For variable stars, the variation is often correlated with color due to the nature of the stellar pulsation. However, for AGNs, the observed variability in the light curve does not necessarily correlate in g and i at the same moment in time as time delays between the g-and i-band continuum fluxes have been observed (e.g., Shappee et al 2014;Fausnaugh et al 2016Fausnaugh et al , 2018Homayouni et al 2019;Cackett et al 2020). Thus, we chose not to combine the g and i data sets in the construction of the J index.…”