Revealing the structure of the lensed quasar Q 0957+561: I. Accretion disk size

C. Fian, E. Mediavilla, J. Jiménez-Vicente, V. Motta, J. A. Muñoz, D. Chelouche, P. Goméz-Alvarez, K. Rojas, A. Hanslmeier

Research output: Contribution to journalArticlepeer-review


Aims. We aim to use signatures of microlensing induced by stars in the foreground lens galaxy to infer the size of the accretion disk in the gravitationally lensed quasar Q 0957+561. The long-term photometric monitoring of this system (which so far has provided the longest available light curves of a gravitational lens system) permits us to evaluate the impact of uncertainties on our recently developed method (controlled by the distance between the modeled and the experimental magnitude difference histograms between two lensed images), and thus to test the robustness of microlensing-based disk-size estimates. Methods. We analyzed the well-sampled 21-year GLENDAMA optical light curves of the double-lensed quasar and studied the intrinsic and extrinsic continuum variations. Using accurate measurements for the time delay between the images A and B, we modeled and removed the intrinsic quasar variability, and from the statistics of microlensing magnifications we used a Bayesian method to derive the size of the region emitting the continuum at rest=2558 Å. Results. Analysis of the Q 0957+561 R-band light curves show a slow but systematic increase in the brightness of the B relative to the A component during the past ten years.

Original languageEnglish
Article numberA70
JournalAstronomy and Astrophysics
StatePublished - 1 Oct 2021

Bibliographical note

Publisher Copyright:
© ESO 2021.


  • Accretion
  • Gravitational lensing: micro
  • Quasars: individual: Q 0957+561
  • accretion disks

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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