The blazar S4 0954+65: the new activity period after 15-months of quiet state
ATel #17880; V. V. Vlasyuk, O. I. Spiridonova (Special Astrophysical Observatory of the Rus. Ac. Sci.)
on 6 Jul 2026; 23:05 UT
Credential Certification: Alexander Moskvitin (mosk@sao.ru)
We continued to monitor the blazar S4 0954+65 throughout the year. Our 1 meter and 0.5 meter reflectors were used in this observation campaign.
Previous maxima of its brightness were found in November 2023 (R=13.22, ATel #16331) and in February 2025 (r~13.9, archive ZTF). After some near-quiet state at the levels between R~15.5 and R~16.5 mag (period between February and June) the flux of S4 0954+65 became higher by ~1 mag for 1 day after rapid brightening, reaching a value of 15.1 mag at MJD=61209.9.
After a 10-day period with flux variation between R=15.1 and 15.5 mag, S4 0954+65 undergo 5 days of the highest activity over the last 15 months. Its brightness exceeded R=14.8 mag on June 30 (MJD=61221.8). The maximum flux for S4 0954+65 was found around MJD=61224.0 and was R=13.80 mag. During the last 2 nights --- 3/4 July and 4/5 July the blazar became fainter up to R=14.6 mag.
Our whole-night monitoring of the blazar behaviour across the last nights revealed a strong intra-night variability (INV) --- up to a flux increasing by 0.5 mag within 3.5 hours (epoch MJD=61223.8-61224). More accurate analysis of INV is in the process of being completed.
Most of the data was obtained in good weather (seeing better 2 arcsec and normal transparency) and has a typical accuracy of about 0.015 mag even in the presence of a bright lunar sky.
The further optical monitoring of the blazar S4 0954+65 is in progress.
