Observational determination of the time delays in gravitational lens system Q2237+0305

Abstract

We present new brightness monitoring observations of the 4 components of gravitationally lensed system Q2237+0305, which show detection of an intrinsic quasar brightness fluctuation at a time of subdued microlensing activity, between June 27 and October 12, 2003. These data were used to determine the time delays between the arrivals of the four images. The measured delays are τ BA ≈ −6, τ CA ≈ 35, and τ DA ≈ 2 h, so they confirm that the long history of brightness monitoring has produced significant detection of microlensing. However the error bars associated with the delays, of order 2 days, are too large to discriminate between competing macro-imaging models. Moreover, our simulations show that for the amplitude of this intrinsic fluctuation and for photometric errors intrinsic to optical monitoring from our 1.5-m telescope or from the OGLE monitoring, a daily sampled brightness record cannot produce reliable lags for model discrimination. We use our simulations to devise a strategy for future delay determination with optical data. Nevertheless, we regard these first estimates to be significant, since they are the first direct measurements of time delays made for this system from ground-based observations in the visual wavelengths. The detected highly correlated fluctuations of the four quasar images provide an extra confirmation of the gravitational-lens nature of Q2237+0305, and give observational justification to the extensive literature which attributes the quasar's previously observed brightness fluctuations to microlensing.

Adaptive PSF fitting – a highly performing photometric method and light curves of the GLS H1413+117: time delays and micro-lensing effects

“…The micro-lensing rate measured for the A, B, C components, on average, corresponds to the characteristic rate of micro-lensing 10 −4 mag d −1 reported for other known gravitationally lensed quasars (Gaynullina et al 2005;Vakulik et al 2006;Goicoechea & Shalyapin 2010;Tsvetkova et al 2010;Ricci et al 2011). …”

“…The long-term light curves indicate the presence of micro-lensing effects, sometimes displaying a large amplitude with respect to by micro-lensing with induced variability at the level of 10 −4 mag d −1 (Gaynullina et al 2005;Vakulik et al 2006;Goicoechea & Shalyapin 2010;Tsvetkova et al 2010). But here we found out one of the fastest micro-lensing effects with a rate of 10 −3 mag d The flux slope of the B component in 2003 is smaller than those of the other components.…”

Q2237+0305 in X-rays: spectra and variability with XMM-Newton

“…In the case of Q2237+0305, the detection of X-ray variability is especially important because it may lead to a direct estimate of the gravitational time-delays that are a significant characteristic of lensed systems. The model prediction of Δτ between different Einstein Cross images is of the order of hours (Schmidt et al 1998), whereas the optical data may provide time-delay values that are accurate to only 1-2 days (Vakulik et al 2006). The only observational estimate of the shortest time-delay is obtained by cross-correlating the X-ray lightcurves from different images of Q2237+0305 (Dai et al 2003) of the Chandra observations: here all four X-ray images of this quasar have been resolved and sufficient variability has been reported (the difference between total fluxes during the first and the second Chandra observations is close to 20% of the averaged value).…”

Analytical Methods in Gravitational Microlensing

“…Here we compare the light curves for Gaussian, PL, LD, AD, and AD1 source models with brightness distributions from Section 3.3 The simulations were performed for a set of 100 random realizations of microlensing field with optical depth σ = 0.3 in order to have possibility to compare with some of the results of papers [47][48][49][50]. All source models had the same half-brightness radius, the light curves for all source models have been calculated for the same microlensing fields.…”