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Reverberation Mapping of the Continuum Source in Active Galactic Nuclei

Fausnaugh, Michael Martin

Abstract Details

2017, Doctor of Philosophy, Ohio State University, Astronomy.
I present results from a monitoring campaign of 11 active galactic nuclei (AGN) conducted in Spring of 2014. I use the reverberation mapping method to probe the interior structures of the AGN, specifically the broad line regions (BLRs) and accretion disks. One of these AGN, NGC~5548, was also subject to multi-wavelength (X-ray, UV, optical, and near-IR) monitoring using 25 ground-based telescopes and four space-based facilities. For NGC~5548, I detect lags between the continuum emission at different wavelengths that follow a trend consistent with the prediction for continuum reprocessing by an accretion disk with temperature profile $T \propto R^{-3/4}$. However, the lags imply a disk radius that is 3 times larger than the prediction from standard thin-disk models. The lags at wavelengths longer than the {\it V} band are also equal to or greater than the lags of high-ionization-state emission lines (such as He\,{\sc ii}\,$\lambda 1640$ and $\lambda 4686$), suggesting that the continuum-emitting source is of a physical size comparable to the inner broad-line region. Using optical spectra from the Large Binocular Telescope, I estimate the bias of the interband continuum lags due to BLR emission observed in the filters, and I find that the bias for filters with high levels of BLR contamination ($\sim\! 20\%$) can be important for the shortest continuum lags. This likely has a significant impact on the {\it u} and {\it U} bands owing to Balmer continuum emission. I then develop a new procedure for the internal (night-to-night) calibration of time series spectra that can reach precisions of $\sim\! 1$ millimagnitude and improves traditional techniques by up to a factor of 5. At this level, other systematic issues (e.g., the nightly sensitivity functions and Fe{\sc ii} contamination) limit the final precision of the observed light curves. Using the new calibration method, I next present the data and first results from the optical spectroscopic monitoring component of the reverberation mapping campaign. Five AGN were sufficiently variable to measure continuum-H$\beta$ lags and super-massive black hole masses: MCG+08-11-011, NGC\,2617, NGC\,4051, 3C\,382, and Mrk\,374. I also obtain H$\gamma$ and \heii\ lags for all objects except 3C\,382. The \heii\ lags indicate radial stratification of the BLR, and the masses derived from different emission lines are in general agreement. The relative responsivities of these lines to continuum variations are also in qualitative agreement with photoionization models. Finally, I measure optical continuum lags for the two most variable targets, MCG+08-11-011 and NGC\,2617. I again find lags consistent with geometrically thin accretion-disk models that have temperature profiles $T \propto R^{-3/4}$. The observed lags are larger than predictions based on standard thin-disk theory by factors of 3.3 for MCG+08-11-011 and 2.3 for NGC\,2617. Using a physical model, these differences can be explained if the mass accretion rates are larger than inferred from the optical continuum luminosity by a factor of 4.3 in MCG+08-11-011 and a factor of 1.3 in NGC\,2617. While the X-ray variability in NGC\,2617 precedes the UV/optical variability, the long 2.6 day lag is problematic for coronal reprocessing models.
Brad Peterson (Advisor)
Chris Kochanek (Committee Member)
Richard Pogge (Committee Member)
Timothy Plageman, Jr (Committee Member)
401 p.

Recommended Citations

Citations

  • Fausnaugh, M. M. (2017). Reverberation Mapping of the Continuum Source in Active Galactic Nuclei [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1494244528720735

    APA Style (7th edition)

  • Fausnaugh, Michael. Reverberation Mapping of the Continuum Source in Active Galactic Nuclei. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1494244528720735.

    MLA Style (8th edition)

  • Fausnaugh, Michael. "Reverberation Mapping of the Continuum Source in Active Galactic Nuclei." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1494244528720735

    Chicago Manual of Style (17th edition)