Revisiting the Einstein Cross with X-shooter spectra: New estimates of accretion disk parameters and broad emission line profiles from microlensing
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 $20000$ mathringA), 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 rs, assuming a thin-disk model with a power-law function of the form rs ∝ λp. 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 rs=4.9+2.3−2.6 √(M/0.3M⊙) (lt-day) and p=0.77+0.47−0.28, respectively, reinforcing a departure from the standard accretion disk model ($ T \propto r_s^{-3/4}$).
Versions
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BibTeX
@misc{jereznicurcar2026revisiting,
title = {{Revisiting the Einstein Cross with X-shooter spectra: New estimates of accretion disk parameters and broad emission line profiles from microlensing}},
author = {R. Jerez-Nicurcar and A. Esteban-Gutiérrez and V. Motta and E. Mediavilla},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.12448},
eprint = {2611.12448},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.12448},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Revisiting the Einstein Cross with X-shooter spectra: New estimates of accretion disk parameters and broad emission line profiles from microlensing
AU - R. Jerez-Nicurcar
AU - A. Esteban-Gutiérrez
AU - V. Motta
AU - E. Mediavilla
PY - 2026
DA - 2026/11/09
PB - arXiv
DO - 10.48550/arxiv.2611.12448
UR - https://arxiv.org/abs/2611.12448
AB - 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 $20000$ mathringA), 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 ∝ λ^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 r_s=4.9^+2.3_−2.6 √(M/0.3M_⊙) (lt-day) and p=0.77^+0.47_−0.28, respectively, reinforcing a departure from the standard accretion disk model ($ T \propto r_s^{-3/4}$).
ER -