Revisiting the Einstein Cross with X-shooter spectra: New estimates of accretion disk parameters and broad emission line profiles from microlensing
Year: 2026
Type: article
Abstract: We present a spectroscopic study of the lensed quasar Q2237+0305, the Einstein Cross, assessing the best wavelength coverage to date with the X-shooter instrument (from 3000 to 20000 Å), and thus improving the available spectroscopic data for this system. Using as a reference the characteristic emission lines for each quasar macro-image, we estimate the chromatic microlensing effect between pairs of images and calculate the extinction curve, confirming no significant differences between spectra C and A caused by extinction in the lens galaxy. In addition, we model the accretion disk characterized by a temperature profile with logarithmic slope 1/p and size r_s, assuming a thin-disk model with a power-law function of the form r_s ∝ łambdaup^p. To do this, we calculated a set of three chromatic microlensing measurements compiling previous estimates from the literature to test the wavelength dependence. This temperature profile was also compared to the canonical thin-disk model with p=4/3. Finally, we estimated the likelihood between the disk model and the observed data collected from multiple epochs through mock microlensing magnification maps and determined the probability density functions of each parameter from a Bayesian analysis. As a result, our estimated values for the accretion disk size and its exponential index are s =4.9^ +2.3 _ -2.6 (lt-day) and p=0.77^ +0.47 _ -0.28 , respectively, reinforcing a departure from the standard accretion disk model ($ T ∝ r_s^ -3/4 $).
Source: Astronomy and Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W7223115586