Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XIII. Ultraviolet Time Lag of H$\beta$ Emission in Mrk 142

TL;DR

This study measures the UV-to-Hβ emission line time lag in Mrk 142, revealing insights into the broad-line region and continuum driving mechanisms in highly accreting active galactic nuclei.

Contribution

First simultaneous UV and optical reverberation mapping of Mrk 142, establishing the UV continuum as the primary driver of broad-line region variability.

Findings

UV-to-Hβ lag of approximately 8.7 days in Mrk 142

UV continuum is closer to the true driving source than optical

Black hole mass estimated at about 2.1 million solar masses

Abstract

We performed a rigorous reverberation-mapping analysis of the broad-line region (BLR) in a highly accreting ($L/L_{\mathrm{Edd}}=0.74-3.4$) active galactic nucleus, Markarian 142 (Mrk 142), for the first time using concurrent observations of the inner accretion disk and the BLR to determine a time lag for the $H\beta$ $\mathrm{\lambda}$4861 emission relative to the ultraviolet (UV) continuum variations. We used continuum data taken with the Niel Gehrels Swift Observatory in the UVW2 band, and the Las Cumbres Observatory, Dan Zowada Memorial Observatory, and Liverpool Telescope in the g band, as part of the broader Mrk 142 multi-wavelength monitoring campaign in 2019. We obtained new spectroscopic observations covering the $H\beta$ broad emission line in the optical from the Gemini North Telescope and the Lijiang 2.4-meter Telescope for a total of 102 epochs (over a period of eight months) contemporaneous to the continuum data. Our primary result states a UV-to-$H\beta$ time lag of $8.68_{-0.72}^{+0.75}$ days in Mrk 142 obtained from light-curve analysis with a Python-based Running Optimal Average algorithm. We placed our new measurements for Mrk 142 on the optical and UV radius-luminosity relations for NGC 5548 to understand the nature of the continuum driver. The positions of Mrk 142 on the scaling relations suggest that UV is closer to the "true" driving continuum than the optical. Furthermore, we obtain $\log(M_{\bullet}/M_{\odot}) = 6.32\pm0.29$ assuming UV as the primary driving continuum.