The FSRQ B2 1308+326: the activity phase at R = 13.44 after gamma-ray flare in December

ATel #16963; V. V. Vlasyuk, O. I. Spiridonova, A. S.Moskvitin (Special Astrophysical Observatory of the Rus. Ac. Sci.)
on 31 Dec 2024; 22:38 UT
Credential Certification: Alexander Moskvitin (mosk@sao.ru)

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The flat spectrum radio quasar B2 1308+326 is demonstrating its activity phase in optical range after powerful flare in gamma-rays, as it was reported by Fermi LAT Collaboration (ATel #16940). The daily averaged gamma-ray flux (E > 100MeV) of (1.3+/-0.2) x 10^-6 photons cm^-2 s^-1 ) on December, 10. This level corresponds to average flux of this source in the 4FGL catalogue multiplied by a factor of 25. Just after this message the outburst of B2 1308+326 up to R = 13.7 on December, 12 was reported in ATel #16951.

This object is observing by SAO RAS team on a regular basis in search of possible correlation between its optical and radio activity events. Two optical reflectors of SAO RAS --- 1 meter and 0.5 meter, equipped by CCD photometers, were used for these studies.

After some dimming of flux between epochs MJD=60658 (R = 13.90) and MJD=60666 (R = 14.50) the blazar begun new stage of re-brightening and reached R = 13.44 according to our estimates at MJD = 60675 (night Dec 30/31). This value is the third one after records of last decade --- R = 12.60 at MJD = 59765 in 2022 and R = 13.36 at MJD = 59958 in 2023.

Typical accuracy of our data was about 0.01 mag. under good transparency and seeing value (FWHM) between 1".5 and 2".5. The estimates of brightness from the both --- 1-m and 0.5-m --- telescopes agree well within their instrumental errors.

As before, for 1-m data we used comparison star F, assuming its R = 14.00 mag. Data from 0.5-m telescope were calibrated using by star C from Smith et al (1985, AJ, 90, 1184). More accurate reduction is necessary. We strongly encourage further multi-wavelength investigations.