NGC 5548 in a Low‐Luminosity State: Implications for the Broad‐Line Region

Bentz, Misty C.; Denney, K. D.; Cackett, Edward M.; Dietrich, M.; Fogel, Jeffrey K. J.; Ghosh, H.; Horne, K.; Kuehn, Charles A.; Minezaki, Takeo; Onken, Christopher A.; Peterson, B. M.; Pogge, Richard W.; Pronik, V. I.; Richstone, D. O.; Сергеев, С. Г.; Vestergaard, M.; Walker, Matthew G.; Yoshii, Yuzuru

doi:10.1086/516724

Cited by 105 publications

(177 citation statements)

References 31 publications

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“…Using almost the same set of light curves from NGC 5548 (we add year 14 and exclude year 13), Cackett & Horne (2006) find a much shallower slope (0.1-0.46) with a luminosity-dependent delay map, in better agreement with the prediction of photoionization models (∼0.23; Korista & Goad 2004). However, their small correction for the host galaxy starlight may artificially flatten their estimate of the slope (Bentz et al 2007). Note that for this experiment we did not make the line-to-continuum scaling coefficient A a function of continuum luminosity in the fit.…”

Section: R Blr -L Relation Of Ngc 5548 Revisitedsupporting

confidence: 52%

An Alternative Approach to Measuring Reverberation Lags in Active Galactic Nuclei

Kochanek

Peterson

2011

ApJ

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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 crosscorrelation 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.

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Section: R Blr -L Relation Of Ngc 5548 Revisitedsupporting

confidence: 52%

An Alternative Approach to Measuring Reverberation Lags in Active Galactic Nuclei

Kochanek

Peterson

2011

ApJ

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381

543

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“…Indeed, the Hβ lag has been measured year-to-year for over a dozen different years, and the lag and the mean luminosity of the AGN are well correlated on yearly timescales, and as noted earlier, the reverberation-based mass is approximately constant with perhaps a weak dependence on luminosity (Bentz et al 2007). Given our goal of comparing SE predictions with reverberation measurements, we have also computed for NGC 5548 the difference between each SE VP and the reverberation VP for the specific year in which the SE observation was made.…”

Section: Effects Of Variabilitymentioning

confidence: 59%

Systematic Uncertainties in Black Hole Masses Determined From Single-Epoch Spectra

Denney¹,

Peterson²,

Dietrich³

et al. 2009

ApJ

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We explore the nature of systematic errors that can arise in measurement of black hole masses from singleepoch (SE) spectra of active galactic nuclei (AGNs) by utilizing the many epochs available for NGC 5548 and PG1229+204 from reverberation mapping (RM) databases. In particular, we examine systematics due to AGN variability, contamination due to constant spectral components (i.e., narrow lines and host galaxy flux), data quality (i.e., signal-to-noise ratio (S/N)), and blending of spectral features. We investigate the effect that each of these systematics has on the precision and accuracy of SE masses calculated from two commonly used line width measures by comparing these results to recent RM studies. We calculate masses by characterizing the broad Hβ emission line by both the full width at half maximum and the line dispersion, and demonstrate the importance of removing narrow emission-line components and host starlight. We find that the reliability of line width measurements rapidly decreases for S/N lower than ∼ 10-20 (per pixel), and that fitting the line profiles instead of direct measurement of the data does not mitigate this problem but can, in fact, introduce systematic errors. We also conclude that a full spectral decomposition to deblend the AGN and galaxy spectral features is unnecessary, except to judge the contribution of the host galaxy to the luminosity and to deblend any emission lines that may inhibit accurate line width measurements. Finally, we present an error budget which summarizes the minimum observable uncertainties as well as the amount of additional scatter and/or systematic offset that can be expected from the individual sources of error investigated. In particular, we find that the minimum observable uncertainty in SE mass estimates due to variability is 0.1 dex for high S/N ( 20 pixel −1 ) spectra.

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“…The aperture of 20 × 28 used in the campaign described by Netzer et al (1990) is larger than the FOV of the HRC camera. We include here the 14 individual measurements reported by Peterson et al (2002) and Bentz et al (2007). 8.…”

Section: Flux Measurementsmentioning

confidence: 99%

THE RADIUS-LUMINOSITY RELATIONSHIP FOR ACTIVE GALACTIC NUCLEI: THE EFFECT OF HOST-GALAXY STARLIGHT ON LUMINOSITY MEASUREMENTS. II. THE FULL SAMPLE OF REVERBERATION-MAPPED AGNs

Bentz¹,

Peterson²,

Netzer³

et al. 2009

ApJ

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608

808

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We present high-resolution Hubble Space Telescope images of all 35 active galactic nuclei (AGNs) with optical reverberation-mapping results, which we have modeled to create a nucleus-free image of each AGN host galaxy. From the nucleus-free images, we determine the host-galaxy contribution to ground-based spectroscopic luminosity measurements at 5100 Å. After correcting the luminosities of the AGNs for the contribution from starlight, we re-examine the Hβ R BLR -L relationship. Our best fit for the relationship gives a power-law slope of 0.52 with a range of 0.45-0.59 allowed by the uncertainties. This is consistent with our previous findings, and thus still consistent with the naive assumption that all AGNs are simply luminosity-scaled versions of each other. We discuss various consistency checks relating to the galaxy modeling and starlight contributions, as well as possible systematic errors in the current set of reverberation measurements from which we determine the form of the R BLR -L relationship.

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NGC 5548 in a Low‐Luminosity State: Implications for the Broad‐Line Region

Cited by 105 publications

References 31 publications

An Alternative Approach to Measuring Reverberation Lags in Active Galactic Nuclei

An Alternative Approach to Measuring Reverberation Lags in Active Galactic Nuclei

Systematic Uncertainties in Black Hole Masses Determined From Single-Epoch Spectra

THE RADIUS-LUMINOSITY RELATIONSHIP FOR ACTIVE GALACTIC NUCLEI: THE EFFECT OF HOST-GALAXY STARLIGHT ON LUMINOSITY MEASUREMENTS. II. THE FULL SAMPLE OF REVERBERATION-MAPPED AGNs

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