AN ALTERNATIVE APPROACH TO MEASURING REVERBERATION LAGS IN ACTIVE GALACTIC NUCLEI

By Y. Zu, C. Kochanek, B. Peterson. 2010

226 citations recorded by the source corpus.

Motivated by recent progress in the statistical modeling of quasar variability, we develop a new approach to measuring emission-line reverberation lags to estimate the size of broad-line regions (BLRs) in active galactic nuclei. Assuming that all emission-line light curves are scaled, smoothed, and displaced versions of the continuum, this alternative approach fits the light curves directly using a damped random walk model and aligns them to recover the time lag and its statistical confidence limits. We introduce the mathematical formalism of this approach and demonstrate its ability to cope with some of the problems for traditional methods, such as irregular sampling, correlated errors, and seasonal gaps. We redetermine the lags for 87 emission lines in 31 quasars and reassess the BLR size–luminosity relationship using 60 Hβ lags. We confirm the general results from the traditional cross-correlation methods, with a few exceptions. Our method, however, also supports a broad range of extensions. In particular, it can simultaneously fit multiple lines and continuum light curves which improves the lag estimate for the lines and provides estimates of the error correlations between them. Determining these correlations is of particular importance for interpreting emission-line velocity–delay maps. We can also include parameters for luminosity-dependent lags or line responses. We use this to detect the scaling of the BLR size with continuum luminosity in NGC 5548.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/8824da62a08e51a936906144dc0d610bb54a167c

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Citations in the corpus

X-ray reverberation around accreting black holes (2014, methodology): “More recently, stochastic modelling and fitting of light curves has been applied to more accurately model the optical reverberation data (Zu et al. 2011; Pancoast et al. 2011).”
Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. IX. 10 New Observations of Reverberation Mapping and Shortened Hβ Lags (2018, methodology): “They successfully measured Hβ lags for 44 SDSS targets mainly using the Bayesian-based modeling code JAVELIN (Zu et al. 2011) and the Continuum REprocessing AGN MCMC software (CREAM; Starkey et al. 2016) instead of the traditional ICCF.13 Interestingly, they, too, found shortened Hβ lags compared wi”
Modelling reverberation mapping data – II. Dynamical modelling of the Lick AGN Monitoring Project 2008 data set (2013, methodology): “For example, Zu et al. (2011) use a CAR(1) process model for the AGN continuum light curve interpolation in their code JAVELIN to measure the time lag between the continuum and an integrated emission line light curve using a top-hat transfer function.”
The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry (2017, methodology): “However, over the past several years, more sophisticated procedures have been developed that model the statistically likely behavior of the light curves in the gaps between observations (e.g., JAVELIN, Zu et al. 2011; and CREAM, Starkey et al. 2016).”
THE MAN BEHIND THE CURTAIN: X-RAYS DRIVE THE UV THROUGH NIR VARIABILITY IN THE 2013 ACTIVE GALACTIC NUCLEUS OUTBURST IN NGC 2617 (2013, methodology): “Reverberation mapping studies ofthe Hβ emission line in local AGN indicate that there is a tight correlation between the AGN continuum linosity at 5100 Å andRBLR (Kaspi et al. 2005; Bentz et al. 2009, 2013; Zu et al. 2011).”
THE SLOAN DIGITAL SKY SURVEY REVERBERATION MAPPING PROJECT: TECHNICAL OVERVIEW (2014, methodology): “In addition, alternative lag measurements to the simple CCF method, such as the Zu et al. (2011) method based on DRW models (e.g., Kelly et al. 2009), can in principle provide a more robust confidence estimation of the detected CCF peaks, and therefore reduce false detections.”
BLACK HOLE MASS ESTIMATES AND EMISSION-LINE PROPERTIES OF A SAMPLE OF REDSHIFT z > 6.5 QUASARS (2013, background): “RM studies of Hβ emission in local AGNs have lead to the discovery of a tight correlation between the AGN continuum luminosity and the distance of the emitting gas (RBLR − L relation; Kaspi et al. 2005; Bentz et al. 2009, 2013; Zu et al. 2011).”
THE LICK AGN MONITORING PROJECT 2011: SPECTROSCOPIC CAMPAIGN AND EMISSION-LINE LIGHT CURVES (2015, methodology): “Additional papers in this series will presentV -band photometric light curves, measurements of broad-line lags and velocity-resolved reverberation using both cross-correlation and JAVELIN (Zu et al. 2011) methodology, black hole virial mass estimates, and BLR dynamical modeling using the methods des”
STELLAR VELOCITY DISPERSION MEASUREMENTS IN HIGH-LUMINOSITY QUASAR HOSTS AND IMPLICATIONS FOR THE AGN BLACK HOLE MASS SCALE (2013, methodology): “Zu et al. (2011) re-measured the time lags in reverberation-mapped AGNs with the SPEAR method and demonstrated its ability to recover accurate time lags.”
REVERBERATION MEASUREMENTS OF THE INNER RADIUS OF THE DUST TORUS IN 17 SEYFERT GALAXIES (2014, methodology): “In this study, we summarize only the procedures; details for the subtraction of the accretion-disk component and the CCF analysis have been reported in previous studies (Suganuma et al. 2006; Koshida et al. 2009), and those for the alternative method are described in Zu et al. (2011).”
REVERBERATION MAPPING RESULTS FOR FIVE SEYFERT 1 GALAXIES (2012, methodology): “Recently, however, Zu et al. (2011) introduced an alternative method of measuring reverberation time lags called Stochastic Process Estimation for AGN Reverberation (SPEAR1), and demonstrated its ability to recover accurate time lags.”
IS QUASAR OPTICAL VARIABILITY A DAMPED RANDOM WALK? (2012, methodology): “We briefly recap the components of the likelihood function here and refer readers to Zu et al. (2011), Koz lowski et al. (2010) and Rybicki & Press (1992) for details.”
THE STRUCTURE OF THE BROAD-LINE REGION IN ACTIVE GALACTIC NUCLEI. I. RECONSTRUCTED VELOCITY-DELAY MAPS (2012, methodology): “To provide stronger constraints on the driving light curve model, we ran our full continuum light curves (including both spectroscopic and photometric data) through the JAVELIN modeling software of Zu et al. (2011).”