Categorías
A&A HIGHLIGHTS

Changing-look of the delay-corrected spectral flux ratio of SDSS J1001+5027

We conducted a long-term optical monitoring of the doubly-imaged gravitationally lensed quasar SDSS J1001+5027 consisting of spectrophotometric observations separated by Δt ∼120 days (time delay between both quasar images) and test/auxiliary data. This monitoring approach allowed us to reliably find a strong microlensing-induced chromatic variation of the quasar continuum in the period
2022−2025. The ongoing microlensing event has caused a dramatic changing-look of the delay-corrected spectral flux ratio in 2025 (see paper). The current status of this flux ratio is being tested through observations with the Liverpool Telescope in January and May 2026.

Delay-corrected spectral flux ratio of SDSS J1001+5027 using the SPectrograph for the Rapid Acquisition of Transients (SPRAT) on the Liverpool Telescope at 25 epochs. We also show the delay-corrected r-band flux ratio (filled circles), and the single-epoch
spectral flux ratio from Gemini North/GMOS (black line) and Keck/LRIS (deep purple line). The three horizontal strips correspond to the Civ (purple), Ciii] (blue), and K-band (grey) flux ratios, which are used to highlight the macrolens flux ratio.