Continued broadband radio and optical brightening and record-high 22 GHz and R band flux density of 3C 138

The RATAN-600 and RT-32 light curves of 3C138 at 2-22 GHz 

https://rat.sao.ru/scientific-results/radio-flare-in-css-quasar-3c-138/

Yu. V. Sotnikova, T. V. Mufakharov, V. V. Vlasyuk, Tao An, O. I. Spiridonova, A. K. Erkenov, R.Yu. Udovitskij, T. A. Semenova, Yu. A. Kovalev, Yu. Y. Kovalev, A.V. Popkov, M. A. Kharinov,  I. A. Rahimov, T. S. Andreeva

We report continued long-term broadband radio and optical brightening of the compact steep-spectrum (CSS) quasar 3C 138, with the variability amplitude increasing toward higher frequencies. In addition to earlier reports of enhanced radio emission (ATel #17077 and #17104), new RATAN-600 (SAO RAS) observations show a record-high flux density at 22.3 GHz of 3.4 ± 0.2 Jy in 2025 November 15, exceeding the previous maximum of 2.7 ± 0.3 Jy reported in 2024 August. The 11.2-22.3 GHz spectral index (S ∝ ν^α) has flattened over the past three years, indicating progressive spectral hardening at cm wavelengths. In October 2025, the spectral index had become rising and reached the value of +0.1-0.2 on 15-16 November.