HST imaging of four gravitationally lensed quasars

Abstract

We present new HST WFPC3 imaging of four gravitationally lensed quasars: MG 0414+0534; RXJ 0911+0551; B 1422+231; WFI J2026-4536. In three of these systems we detect wavelength-dependent microlensing, which we use to place constraints on the sizes and temperature profiles of the accretion discs in each quasar. Accretion disc radius is assumed to vary with wavelength according to the power-law relationship r ∝ λ p , equivalent to a radial temperature profile of T ∝ r −1/p . The goal of this work is to search for deviations from standard thin disc theory, which predicts that radius goes as wavelength to the power p = 4/3. We find a wide range of power-law indices, from p = 1.4 +0.5 −0.4 in B 1422+231 to p = 2.3 +0.5 −0.4 in WFI J2026-4536. The measured value of p appears to correlate with the strength of the wavelength-dependent microlensing. We explore this issue with mock simulations using a fixed accretion disc with p = 1.5, and find that cases where wavelength-dependent microlensing is small tend to under-estimate the value of p. This casts doubt on previous ensemble singleepoch measurements which have favoured low values using samples of lensed quasars that display only moderate chromatic effects. Using only our systems with strong chromatic microlensing we prefer p > 4/3, corresponding to shallower temperature profiles than expected from standard thin disc theory.

Reconciling the quasar microlensing disc size problem with a wind model of active galactic nucleus

“…This shares a similarity with the suggestion of a flatter disc temperature profile mentioned above, although the physical origin of the flattening has not been linked to disc winds in previous works yet. Observationally, a flattening of temperature profile than the theoretical expectation of 3/4 from the thin-disc model has been confirmed for several microlensing studies of disc structures (e.g., Bate et al 2008;Poindexter, Morgan, & Kochanek 2008;Bate et al 2018). However, a few sources show that the temperature profile could be even steeper than 3/4, although the uncertainty is still very large (e.g., Eigenbrod et al 2008;King & Pounds 2015;Muñoz et al 2016).…”

Constraining quasar structure using high-frequency microlensing variations and continuum reverberation

“…Eigenbrod et al 2008a). Such chromaticity also enables the measurement of quasar accretion disks through single epoch multi-wavelength observations (Bate et al 2008) and although this method may be biased by the strength of the wavelength-dependent microlensing, it is a reliable way to measure the size of accretion disks (Bate et al 2018a). While in many strongly lensed quasars this method yields results in agreement with the thin disk theory (e.g.…”

Gravitational Wave Enhancement as a Tool to Distinguish Dark Matter Halo Profiles

“…Recent successes in gravitational wave detection, (Abbott et al 2016), together with the well documented effect of gravitational lensing (GL) (Bate et al 2018), have given strength to the idea of using general relativity to describe the gravitational field. One of the first complete treatments of the combination of these effects, i.e.…”