Simulating quasar microlensing light curves: High magnification events

¹ Instituto de Astrofísica, Facultad de Ciencias Exactas, Universidad Andres Bello, Av. Fernandez Concha 700, Las Condes, Santiago, Chile
² Institute of Physics, Laboratory of Astrophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
³ Millennium Institute of Astrophysics, Monseñor Nuncio Sotero Sanz 100, Oficina 104, 7500011 Providencia, Santiago, Chile
⁴ The Graduate Center of the City University of New York, 365 Fifth Avenue, New York, NY 10016, USA
⁵ Department of Astrophysics, American Museum of Natural History, Central Park West and 79th Street, NY 10024-5192, USA
⁶ Department of Physics and Astronomy, Lehman College of the CUNY, Bronx, NY 10468, USA

^⋆ Corresponding author: fcneirad@gmail.com

Received: 11 April 2025
Accepted: 4 July 2025

Abstract

Quasar microlensing can be used to constrain important astrophysical properties, such as the accretion disk size and the amount of stars in the lensing galaxy. The associated brightness variations over time, in particular high magnification events (HMEs) and caustic crossings, can yield precise constraints due to their strong dependence on the relative projected velocities of the components and accretion disk size. The next generation of large sky area surveys, such as The Vera Rubin Observatory (LSST) and Euclid, are expected to find and follow-up thousands of lensed quasars from which such events could be identified and observed. In this work we present a characterization and estimation of all HMEs that could potentially be observed, focusing on systems that could be identified by ground based telescopes. From systems whose minimum image separation is at least 1 arcsec, and their second dimmest image is at least 21.5 magnitudes in the i-band (∼560 in the southern or northern sky), we estimate ∼60 HMEs with amplitudes > 0.3 [mag] in the r-band per year. We find that on average, saddle images are approximately four times more likely to host events than minima, and ∼10% (∼50%) of events are caustic crossings for saddles (minima). We also find that HMEs in saddle images can have amplitudes ∼1 − 2 [mag] larger than minima.