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Register a new userA Microlensing Accretion Disk Size Measurement in the Lensed Quasar WFI 2026-4536
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Matthew Cornachione
Publication date
2019
fields
Physics
and research's language is
English
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We use thirteen seasons of R-band photometry from the 1.2m Leonard Euler Swiss Telescope at La Silla to examine microlensing variability in the quadruply-imaged lensed quasar WFI 2026-4536. The lightcurves exhibit ${sim},0.2,text{mag}$ of uncorrelated variability across all epochs and a prominent single feature of ${sim},0.1,text{mag}$ within a single season. We analyze this variability to constrain the size of the quasars accretion disk. Adopting a nominal inclination of 60$^text{o}$, we find an accretion disk scale radius of $log(r_s/text{cm}) = 15.74^{+0.34}_{-0.29}$ at a rest-frame wavelength of $2043,unicode{xC5}$, and we estimate a black hole mass of $log(M_{text{BH}}/M_{odot}) = 9.18^{+0.39}_{-0.34}$, based on the CIV line in VLT spectra. This size measurement is fully consistent with the Quasar Accretion Disk Size - Black Hole Mass relation, providing another system in which the accretion disk is larger than predicted by thin disk theory.
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We present 13 seasons of $R$-band photometry of the quadruply-lensed quasar WFI 2033-4723 from the 1.3m SMARTS telescope at CTIO and the 1.2m Euler Swiss Telescope at La Silla, in which we detect microlensing variability of $sim0.2$ mags on a timescale of $sim$6 years. Using a Bayesian Monte Carlo technique, we analyze the microlensing signal to obtain a measurement of the size of this systems accretion disk of $log (r_s/{rm cm}) = 15.86^{+0.25}_{-0.27}$ at $lambda_{rest} = 2481{rm AA}$, assuming a $60^circ$ inclination angle. We confirm previous measurements of the BC and AB time delays, and we obtain a tentative measurement of the delay between the closely spaced A1 and A2 images of $Delta t_{A1A2} = t_{A1} - t_{A2} = -3.9^{+3.4}_{-2.2}$ days. We conclude with an update to the Quasar Accretion Disk Size - Black Hole Mass Relation, in which we confirm that the accretion disk size predictions from simple thin disk theory are too small.
We compare the microlensing-based continuum emission region size measurements in a sample of 15 gravitationally lensed quasars with estimates of luminosity-based thin disk sizes to constrain the temperature profile of the quasar continuum accretion region. If we adopt the standard thin disk model, we find a significant discrepancy between sizes estimated using the luminosity and those measured by microlensing of $log(r_{L}/r_{mu})=-0.57pm0.08,text{dex}$. If quasar continuum sources are simple, optically thick accretion disks with a generalized temperature profile $T(r) propto r^{-beta}$, the discrepancy between the microlensing measurements and the luminosity-based size estimates can be resolved by a temperature profile slope $0.37 < beta < 0.56$ at $1,sigma$ confidence. This is shallower than the standard thin disk model ($beta=0.75$) at $3,sigma$ significance. We consider alternate accretion disk models that could produce such a temperature profile and reproduce the empirical continuum size scaling with black hole mass, including disk winds or disks with non-blackbody atmospheres.
We present three complete seasons and two half-seasons of SDSS r-band photometry of the gravitationally lensed quasar SBS 0909+532 from the U.S. Naval Observatory, as well as two seasons each of SDSS g-band and r-band monitoring from the Liverpool Robotic Telescope. Using Monte Carlo simulations to simultaneously measure the systems time delay and model the r-band microlensing variability, we confirm and significantly refine the precision of the systems time delay to Delta t_{AB} = 50^{+2}_{-4} days, where the stated uncertainties represent the bounds of the formal 1sigma confidence interval. There may be a conflict between the time delay measurement and a lens consisting of a single galaxy. While models based on the Hubble Space Telescope astrometry and a relatively compact stellar distribution can reproduce the observed delay, the models have somewhat less dark matter than we would typically expect. We also carry out a joint analysis of the microlensing variability in the r- and g-bands to constrain the size of the quasars continuum source at these wavelengths, obtaining log[(r_{s,r}/cm) [cos{i}/0.5]^{1/2}] = 15.3 pm 0.3 and log[(r_{s,g}/cm) [cos{i}/0.5]^{1/2}] = 14.8 pm 0.9, respectively. Our current results do not formally constrain the temperature profile of the accretion disk but are consistent with the expectations of standard thin disk theory.
We present eight monitoring seasons of the four brightest images of the gravitational lens SDSS J1004+4112 observed between December 2003 and October 2010. Using measured time delays for the images A, B and C and the model predicted time delay for image D we have removed the intrinsic quasar variability, finding microlensing events of about 0.5 and 0.7 mag of amplitude in the images C and D. From the statistics of microlensing amplitudes in images A, C, and D, we have inferred the half-light radius (at {lambda} rest = 2407 {AA}) for the accretion disk using two different methods, $R_{1/2}=8.7^{+18.5}_{-5.5} sqrt{M/0.3 M_odot}$ (histograms product) and $R_{1/2} = 4.2^{+3.2}_{-2.2} sqrt{M/0.3 M_odot}$ light-days ($chi^2$). The results are in agreement within uncertainties with the size predicted from the black hole mass in SDSS J1004+4112 using the thin disk theory.
Microlensing perturbations to the magnification of gravitationally lensed quasar images are dependent on the angular size of the quasar. If quasar variability at visible wavelengths is caused by a change in the area of the accretion disk, it will affect the microlensing magnification. We derive the expected signal, assuming that the luminosity scales with some power of the disk area, and estimate its amplitude using simulations. We discuss the prospects for detecting the effect in real-world data and for using it to estimate the logarithmic slope of the luminositys dependence on disk area. Such an estimate would provide a direct test of the standard thin accretion disk model. We tried fitting six seasons of the light curves of the lensed quasar HE 0435-1223 including this effect as a modification to the Kochanek et al. (2006) approach to estimating time delays. We find a dramatic improvement in the goodness of fit and relatively plausible parameters, but a robust estimate will require a full numerical calculation in order to correctly model the strong correlations between the structure of the microlensing magnification patterns and the magnitude of the effect. We also comment briefly on the effect of this phenomenon for the stability of time delay estimates.
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