Bayesian analysis of quasar light curves with a running optimal average: new time delay measurements of COSMOGRAIL gravitationally lensed quasars

Donnan, Fergus R.; Horne, K.; Santisteban, J. V. Hernández

doi:10.1093/mnras/stab2832

Cited by 18 publications

(25 citation statements)

References 57 publications

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“…The inter-telescope calibration determines telescope-specific scale factors 𝐴 𝑠 , which can arise from differences in the CCD sensitivities and the filter and telescope transmissions, and additive background flux offsets 𝐵 𝑠 , which may arise from different angular aperture sizes or angular resolution. To optimise the inter-calibration parameters we use P ROA 3 (Donnan et al 2021), which models the underlying lightcurve, 𝑋 (𝑡), as a running optimal average (ROA) that is scaled by a factor 𝐴 𝑠 and shifted by 𝐵 𝑠 to fit the flux data over all epochs for telescope 𝑠:…”

Section: Inter-telescope Calibrationmentioning

confidence: 99%

“…We use P ROA (Donnan et al 2021) to model the flux data of the 7-band LCO lightcurves and determine the inter-band delays. Analysing each year of data separately, we measure delays relative to the 𝑔 -band lightcurve, which has more epochs and higher signalto-noise ratio than the others.…”

Section: P Roamentioning

confidence: 99%

“…This method models all of the lightcurves simultaneously using all of the data available to determine the shape of the variability, providing an advantage over cross-correlation methods that estimate lags from pairs of lightcurves. Full details of the fitting process can be found in Donnan et al (2021).…”

Section: P Roamentioning

confidence: 99%

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Testing Super-Eddington Accretion onto a Supermassive Black Hole: Reverberation Mapping of PG 1119+120

Donnan,

Santisteban,

Horne

et al. 2023

Preprint

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We measure the black hole mass and investigate the accretion flow around the local (𝑧 = 0.0502) quasar PG 1119+120. Spectroscopic monitoring with Calar Alto provides H𝛽 lags and linewidths from which we estimate a black hole mass of log (𝑀 • /M ) = 7.0, uncertain by ∼ 0.4 dex. High cadence photometric monitoring over two years with the Las Cumbres Observatory provides lightcurves in 7 optical bands suitable for intensive continuum reverberation mapping. We identify variability on two timescales. Slower variations on a 100-day timescale exhibit excess flux and increased lag in the 𝑢 band and are thus attributable to diffuse bound-free continuum emission from the broad line region. Faster variations that we attribute to accretion disc reprocessing lack a 𝑢 -band excess and have flux and delay spectra consistent with either 𝜏 ∝ 𝜆 4/3 , as expected for a temperature structure of 𝑇 (𝑅) ∝ 𝑅 −3/4 for a thin accretion disc, or 𝜏 ∝ 𝜆 2 expected for a slim disc. Decomposing the flux into variable (disc) and constant (host galaxy) components, we find the disc SED to be flatter than expected with 𝑓 𝜈 ∼ const. Modelling the SED predicts an Eddington ratio of 𝜆 Edd > 1, where the flat spectrum can be reproduced by a slim disc with little dust extinction or a thin disc which requires more dust extinction. While this accretion is super-Eddington, the geometry is still unclear, however a slim disc is expected due to the high radiation pressure at these accretion rates, and is entirely consistent with our observations.

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Section: Inter-telescope Calibrationmentioning

confidence: 99%

Section: P Roamentioning

confidence: 99%

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Testing Super-Eddington Accretion onto a Supermassive Black Hole: Reverberation Mapping of PG 1119+120

Donnan,

Santisteban,

Horne

et al. 2023

Preprint

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“…In combination with the arrival time difference between the different images of the source, the Hubble constant can be constrained assuming a given cosmological model. Other factors, such as the environment surface mass density, the velocity dispersion of the lensing galaxy, and time-delay microlensing effects, also help characterizing H 0 with precision (e.g., Chen et al 2018;Sluse et al 2019;Tihhonova et al 2020;Millon et al 2020;Donnan et al 2021;Liao 2021;Yıldırım et al 2021). e-mail: lyne.vandevyvere@uliege.be While a gravitational lensing analysis requires many ingredients to perform with the best precision, we focus here on the role of the mass model of the lensing galaxy.…”

Section: Introductionmentioning

confidence: 99%

Consequences of the lack of azimuthal freedom in the modeling of lensing galaxies

Vyvere¹,

Sluse²,

Gomer³

et al. 2022

A&A

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Massive elliptical galaxies can display structures that deviate from a pure elliptical shape, such as a twist of the principal axis or variations in the axis ratio with galactocentric distance. Although satisfactory lens modeling is generally achieved without accounting for these azimuthal structures, the question about their impact on inferred lens parameters remains, in particular, on time delays as they are used in time-delay cosmography. This paper aims at characterizing these effects and quantifying their impact considering realistic amplitudes of the variations. We achieved this goal by creating mock lensing galaxies with morphologies based on two data sets: observational data of local elliptical galaxies, and hydrodynamical simulations of elliptical galaxies at a typical lens redshift. We then simulated images of the lensing systems with space-based data quality and modeled them in a standard way to assess the impact of a lack of azimuthal freedom in the lens model. We find that twists in lensing galaxies are easily absorbed in homoeidal lens models by a change in orientation of the lens up to 10° with respect to the reference orientation at the Einstein radius, and of the shear by up to 20° with respect to the input shear orientation. The ellipticity gradients, on the other hand, can introduce a substantial amount of shear that may impact the radial mass model and consequently bias H0, up to 10 km s−1 Mpc−1. However, we find that light is a good tracer of azimuthal structures, meaning that direct imaging should be capable of diagnosing their presence. This in turn implies that such a large bias is unlikely to be unaccounted for in standard modeling practices. Furthermore, the overall impact of twists and ellipticity gradients averages out at a population level. For the galaxy populations we considered, the cosmological inference remains unbiased.

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“…In the parametric family of techniques, examples include Hojjati et al (2013) who perform Gaussian Process (GP) regression to model the intrinsic light curve and Tewes et al (2013) who use a free-knot spline technique. More recently, Bag et al (2021) developed a Bayesian method to identify gravitationally lensed Type Ia supernovae (SNe Ia) from unresolved light curves and measure their time delays, and Donnan et al (2021) propose a time delay estimation method based on a running optimal average (ROA) model for the light curve data.…”

Section: Introductionmentioning

confidence: 99%

TD-CARMA: Painless, accurate, and scalable estimates of gravitational-lens time delays with flexible CARMA processes

Meyer¹,

Dyk²,

Tak³

et al. 2022

Preprint

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Cosmological parameters encoding our current understanding of the expansion history of the Universe can be constrained by the accurate estimation of time delays arising in gravitationally lensed systems. We propose TD-CARMA, a Bayesian method to estimate cosmological time delays by modelling the observed and irregularly sampled light curves as realizations of a Continuous Auto-Regressive Moving Average (CARMA) process. Our model accounts for heteroskedastic measurement errors and microlensing, an additional source of independent extrinsic long-term variability in the source brightness. The CARMA formulation admits a linear state-space representation, that allows for efficient and scalable likelihood computation using the Kalman Filter. We obtain a sample from the joint posterior distribution of the model parameters using a nested sampling approach. This allows for "painless" Bayesian Computation, dealing with the expected multi-modality of the posterior distribution in a straightforward manner and not requiring the specification of starting values or an initial guess for the time delay, unlike existing methods. In addition, the proposed sampling procedure automatically evaluates the Bayesian evidence, allowing us to perform principled Bayesian model selection. TD-CARMA is parsimonious, and typically includes no more than a dozen unknown parameters. We apply TD-CARMA to three doubly lensed quasars HS 2209+1914, SDSS J1001+5027 and SDSS J1206+4332, estimating their time delays as −21.96±1.448 (6.6% precision), 120.93±1.015 (0.8%), and 111.51±1.452 (1.3%), respectively. A python package, TD-CARMA, is publicly available to implement the proposed method.

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Bayesian analysis of quasar light curves with a running optimal average: new time delay measurements of COSMOGRAIL gravitationally lensed quasars

Cited by 18 publications

References 57 publications

Testing Super-Eddington Accretion onto a Supermassive Black Hole: Reverberation Mapping of PG 1119+120

Testing Super-Eddington Accretion onto a Supermassive Black Hole: Reverberation Mapping of PG 1119+120

Consequences of the lack of azimuthal freedom in the modeling of lensing galaxies

TD-CARMA: Painless, accurate, and scalable estimates of gravitational-lens time delays with flexible CARMA processes

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