The CSS 3C 138: brightness is at the year maxima again

ATel #18093; V. V. Vlasyuk, O. I. Spiridonova (Special Astrophysical Observatory of the Rus. Ac. Sci.)
on 7 Oct 2026; 22:57 UT
Credential Certification: Alexander Moskvitin (mosk@sao.ru)

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The compact steep-spectrum (CSS) quasar 3C 138 exhibits increasing optical activity in October. After reaching local maximum R = 15.44 +/- 0.02 mag at September 12/13 night (MJD 61296.0) (see ATel#18047) the quasar faded to value R = 16.58 +/- 0.01 mag within 10 days. New period of re-brightening started within a few days --- the brightness of 3C138 reached a new maximum R = 15.20 +/- 0.01 mag on October 5/6 night (MJD 61319.0). This value is only 0.05 mags below 3C138 absolute maximum in a course of last December flare. The current slope of the light curve is about -0.15 mag/day, which is as steep as 3C138 light curve brightening in September. Last night (MJD 61320) data gave some fainter flux --- 15.22 +/- 0.01 mags. Probably, the brightening phase of 3C138 is changing by fading ones.

All estimates for the 3C 138 re-brightening phase were provided with 1-meter and 0.5-meter SAO RAS optical reflectors. Their results are coinciding within internal accuracy (0.01--0.02 mags). They were calibrated using our own secondary standards in the 3C 138 field.

More accurate data reduction is necessary. We strongly encourage further multi-wavelength observations.