Testing Super-Eddington Accretion onto a Supermassive Black Hole: Reverberation Mapping of PG 1119+120

Abstract

We measure the black hole mass and investigate the accretion flow around the local (𝑧 = 0.0502) quasar PG 1119+120. Spectroscopic monitoring with Calar Alto provides H𝛽 lags and linewidths from which we estimate a black hole mass of log (𝑀 • /M ) = 7.0, uncertain by ∼ 0.4 dex. High cadence photometric monitoring over two years with the Las Cumbres Observatory provides lightcurves in 7 optical bands suitable for intensive continuum reverberation mapping. We identify variability on two timescales. Slower variations on a 100-day timescale exhibit excess flux and increased lag in the 𝑢 band and are thus attributable to diffuse bound-free continuum emission from the broad line region. Faster variations that we attribute to accretion disc reprocessing lack a 𝑢 -band excess and have flux and delay spectra consistent with either 𝜏 ∝ 𝜆 4/3 , as expected for a temperature structure of 𝑇 (𝑅) ∝ 𝑅 −3/4 for a thin accretion disc, or 𝜏 ∝ 𝜆 2 expected for a slim disc. Decomposing the flux into variable (disc) and constant (host galaxy) components, we find the disc SED to be flatter than expected with 𝑓 𝜈 ∼ const. Modelling the SED predicts an Eddington ratio of 𝜆 Edd > 1, where the flat spectrum can be reproduced by a slim disc with little dust extinction or a thin disc which requires more dust extinction. While this accretion is super-Eddington, the geometry is still unclear, however a slim disc is expected due to the high radiation pressure at these accretion rates, and is entirely consistent with our observations.

Revisiting UV/optical continuum time lags in AGN

“…Intense, multiwavelength, monitoring campaign using spacebased and ground-based telescopes confirmed the presence of correlation between AGN light curves in various UV/optical bands where the time delay increases as function of wavelength (e.g. Edelson et al 2015 ;Fausnaugh et al 2016 ;Cackett et al 2018 ; E-mail: ekammoun@irap.omp.eu and ekammoun.astro@gmail.com McHardy et al 2018 ;Edelson et al 2019 ;Cackett et al 2020 ;Hern ández Santisteban et al 2020 ;Pahari et al 2020 ;Kara et al 2021 ;Vincentelli et al 2021Vincentelli et al , 2022Donnan et al 2023 ;Kara et al 2023 ;McHardy et al 2023 ). In many of these cases modelling the data assuming thermal reverberation was able to explain the shape of the time lags as function of wavelength (time-lag spectra), while underpredicting its amplitude (see e.g.…”