Liverpool-Maidanak monitoring of the Einstein Cross in 2006$-$2019. I. Light curves in the $gVrRI$ optical bands and microlensing signatures

Abstract

Quasar microlensing offers a unique opportunity to resolve tiny sources in distant active galactic nuclei and study compact object populations in lensing galaxies. We therefore searched for microlensing-induced variability of the gravitationally lensed quasar QSO 2237+0305 (Einstein Cross) using 4374 optical frames taken with the 2.0 m Liverpool Telescope and the 1.5 m Maidanak Telescope. These $gVrRI$ frames over the 2006$-$2019 period were homogeneously processed to generate accurate long-term multi-band light curves of the four quasar images A-D. Through difference light curves, we found strong microlensing signatures. We then focused on the analytical modelling of two putative caustic-crossing events in image C, finding compelling evidence that this image experienced a double caustic crossing. Additionally, our overall results indicate that a standard accretion disc accounts reasonably well for the brightness profile of UV continuum emission sources and for the growth in source radius when the emission wavelength increases: $R_{\lambda }\propto {\lambda }^{\alpha }$, $\alpha$ = 1.33 $\pm$ 0.09. However, we caution that numerical microlensing simulations are required before firm conclusions can be reached on the UV emission scenario because the $VRI$-band monitoring during the first caustic crossing and one of our two $\alpha$ indicators lead to a few good solutions with $\alpha \approx$ 1.

Accepted to A&A; 10 pages, 10 long tables (Tables 4-8 and 10-14) are available at the CDS; correction of affiliation

References in corpus (4)

• The Spatial Structure of An Accretion Disk
• Microlensing variability in the gravitationally lensed quasar QSO 2237+0305 = the Einstein Cross. II. Energy profile of the accretion disk
• The multiple quasar Q2237+0305 under a microlensing caustic
• Is there a caustic crossing in the lensed quasar Q2237+0305 observational data record?

Cited by in corpus (6)

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• Evidence for a milliparsec-separation Supermassive Binary Black Hole with quasar microlensing
• Simulating quasar microlensing light curves: High magnification events
• Geometry and kinematics of the broad emission line region in the lensed quasar Q2237+0305
• Joining forces: 30 years of optical monitoring of the Einstein Cross