The CSS 3C 138: secondary R band maximum after 40 days
ATel #17540; V. V. Vlasyuk, O. I. Spiridonova (Special Astrophysical Observatory of the Rus. Ac. Sci.)
on 11 Dec 2025; 21:32 UT
Credential Certification: Alexander Moskvitin (mosk@sao.ru)
Subjects: Optical, Quasar
Referred to by ATel #: 17645
The compact steep-spectrum (CSS) quasar 3C 138 demonstrate enhanced activity in optical
range (R band) since 2025 September. As we reported in ATel #17539 its brightness achieved 2
mJy level (R~15.45 +/- 0.01 mag) (October 31) and faded after with a slope -0.03 mJy/day. But
after stabilization of flux between November 24 and November 29 the quasar started new phase
of re-brightening and reached 2 mJy level again (R~15.49 +/- 0.02 mag) at December 11/12 night.
The slope of light curve was 2 times steeper in comparison with fading phase --- about 0.06
mJy/day, which is similar to behavior of 3C 138 in 2025 October.
All estimates for the 3C 138 re-brightening phase were provided with 0.5-meter SAO RAS
telescope. They were calibrated using our own secondary standards in the 3C 138 field.
More accurate reduction is necessary. We strongly encourage further multi-wavelength
observations.
