Revealing the structure of the lensed quasar Q 0957+561. I. Accretion disk size
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Gravitational lensing: microQuasars: individual: Q 0957+561Accretion, accretion disks
C. Fian... [et al.]. Revealing the structure of the lensed quasar Q 0957+561 I. Accretion disk size. A&A, 654 (2021) A70. DOI: [https://doi.org/10.1051/0004-6361/202039854]
SponsorshipTel Aviv University; University of Haifa through a DFG HA3555-14/1; Spanish MINECO AYA2016-79104-C3-1-P AYA2016-79104-C3-3-P; Generalitat Valenciana; European Commission; General Electric 2020/085; Spanish Ministerio de Economia y Competividad AYA2017-84897-P; European Commission; Junta de Andalucia FQM-108; Swiss National Science Foundation (SNSF); Centro de Astrofisica de Valparaiso
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 di fference 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 lambda(rest) = 2558 angstrom. 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. The relatively low strength of the magnitude differences between the images indicates that the quasar has an unusually big optical accretion disk of half-light radius: R-1/2 = 17.6 +/- 6.1 root M/0/3 M-circle dot lt-days.