A degeneracy in DRW modelling of AGN light curves

Kozłowski, S.

doi:10.1093/mnras/stw819

Cited by 42 publications

(25 citation statements)

References 10 publications

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“…Rather than linearly interpolating between light curve points, JAVELIN models the light curves as an autoregressive process using a DRW model and treats the emission-line light curves as scaled, shifted, and smoothed versions of the continuum light curves. The DRW model is observed to be a good description of quasar variability within the time regime relevant to our study (e.g., Kelly et al 2009;Kozłowski et al 2010Kozłowski et al , 2016MacLeod et al 2010MacLeod et al , 2012, so it is an effective prior to describe the light curve between observations. JAVELIN builds a model of both light curves and simultaneously fits a transfer function, maximizing the likelihood of the model and computing uncertainties using the (Bayesian) Markov chain Monte Carlo technique.…”

Section: Lag Measurementsmentioning

confidence: 86%

The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry

Grier

Trump

Shen

et al. 2017

ApJ

194

259

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We present reverberation mapping results from the first year of combined spectroscopic and photometric observations of the Sloan Digital Sky Survey Reverberation Mapping Project. We successfully recover reverberation time delays between the g+i band emission and the broad Hβ emission line for a total of 44 quasars, and for the broad Hα emission line in 18 quasars. Time delays are computed using the JAVELIN and CREAM software and the traditional interpolated cross-correlation function (ICCF): using well-defined criteria, we report measurements of 32 Hβ and 13 Hα lags with JAVELIN, 42 Hβ and 17 Hα lags with CREAM, and 16 Hβ and eight Hα lags with the ICCF. Lag values are generally consistent among the three methods, though we typically measure smaller uncertainties with JAVELIN and CREAM than with the ICCF, given the more physically motivated light curve interpolation and more robust statistical modeling of the former two methods. The median redshift of our Hβ-detected sample of quasars is 0.53, significantly higher than that of the previous reverberation mapping sample. We find that in most objects, the time delay of the Hα emission is consistent with or slightly longer than that of Hβ. We measure black hole masses using our measured time delays and line widths for these quasars. These black hole mass measurements are mostly consistent with expectations based on the local M BH -* s relationship, and are also consistent with single-epoch black hole mass measurements. This work increases the current sample size of reverberation-mapped active galaxies by about two-thirds and represents the first large sample of reverberation mapping observations beyond the local universe (z<0.3).

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Section: Lag Measurementsmentioning

confidence: 86%

The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry

Grier

Trump

Shen

et al. 2017

ApJ

194

259

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“…Only two of the remaining seven sources (J005448+225123 and J010234+050853) have sufficiently short rise times to be considered a viable TDE event(the other five candidates all have a longer rise time than fall time that is not the expected profile). From the spectra of these quasars, we measure Mg II equivalent widths of 1100 km s −1 (J005448+225123) and 4500 km s −1 (J010234+050853), respectively, which give virial black hole masses of log 10 (M/M ) = 7.8 and 8.9 using Kozlowski (2016b). Assuming that the viscous time for the accretion disc is 100 times longer than the orbital period, Guillochon & Ramirez-Ruiz (2015) find that the majority of events associated with black holes below a fiducial mass of log 10 (M/M ) = 7.0 are slowed.…”

Section: Slow Tdesmentioning

confidence: 99%

Understanding extreme quasar optical variability with CRTS – I. Major AGN flares

Graham¹,

Djorgovski²,

Drake³

et al. 2017

Monthly Notices of the Royal Astronomical Society

119

133

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There is a large degree of variety in the optical variability of quasars and it is unclear whether this is all attributable to a single (set of) physical mechanism(s). We present the results of a systematic search for major flares in active galactic nucleus (AGN) in the Catalina Real-time Transient Survey as part of a broader study into extreme quasar variability. Such flares are defined in a quantitative manner as being atop of the normal, stochastic variability of quasars. We have identified 51 events from over 900 000 known quasars and high-probability quasar candidates, typically lasting 900 d and with a median peak amplitude of m = 1.25 mag. Characterizing the flare profile with a Weibull distribution, we find that nine of the sources are well described by a single-point single-lens model. This supports the proposal by Lawrence et al. that microlensing is a plausible physical mechanism for extreme variability. However, we attribute the majority of our events to explosive stellar-related activity in the accretion disc: superluminous supernovae, tidal disruption events and mergers of stellar mass black holes.

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“…However, there is evidence that the DRW process is no longer appropriate on a short time scale of days (Mushotzky et al 2011;Kasliwal et al 2015;Kozlowski 2016). This impedes the application of our approach in recovering very fine structures (on a timescale of days) in the transfer function.…”

Section: Mrk 817mentioning

confidence: 98%

A Non-Parametric Approach to Constrain the Transfer Function in Reverberation Mapping

Wang

Bai

2016

ApJ

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Broad emission lines of active galactic nuclei stem from a spatially extended region (broad-line region, BLR) that is composed of discrete clouds and photoionized by the central ionizing continuum. The temporal behaviors of these emission lines are blurred echoes of the continuum variations (i.e., reverberation mapping, RM) and directly reflect the structures and kinematic information of BLRs through the so-called transfer function (also known as the velocity-delay map). Based on the previous works of Rybicki & Press and Zu et al., we develop an extended, non-parametric approach to determine the transfer function for RM data, in which the transfer function is expressed as a sum of a family of relatively displaced Gaussian response functions. Therefore, arbitrary shapes of transfer functions associated with complicated BLR geometry can be seamlessly included, enabling us to relax the presumption of a specified transfer function frequently adopted in previous studies and to let it be determined by observation data. We formulate our approach in a previously well-established framework that incorporates the statistical modeling of the continuum variations as a damped random walk process and takes into account the long-term secular variations which are irrelevant to RM signals. The Application to RM data shows the fidelity of our approach.

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A degeneracy in DRW modelling of AGN light curves

Cited by 42 publications

References 10 publications

The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry

The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry

Understanding extreme quasar optical variability with CRTS – I. Major AGN flares

A Non-Parametric Approach to Constrain the Transfer Function in Reverberation Mapping

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