MASTER optical follow-up observations of blazars TXS 1700+685

ATel #14643; K. Zhirkov, V. Lipunov, V. Kornilov, P. Balanutsa, I. Gorbunov, E. Gorbovskoy, O. Gress, N. Tyurina, A. Kuznetsov, V. Vladimirov, D. Vlasenko, D. Zimnukhov, V. Senik, V. Shumkov, A. Chasovnikov, E. Minkina, V. Topolev, D. Kuvshinov, T. Pogrosheva, V. Shumkov (Lomonosov Moscow State University), D/A/H/Buckley (SAAO), R. Podesta, F. Podesta, C. Lopez, C. Francile (Observatorio Astronomico Felix Aguilar OAFA), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias), N. Budnev, O. Ershova (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory) A. Gabovich, V. Yurkov (Blagoveschensk Educational State University)
on 19 May 2021; 10:47 UT
Credential Certification: Nataly Tyurina (tiurina@sai.msu.ru)

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MASTER-NET reports on the enhanced optical activity and significant intranight variability of the gamma-ray flaring blazars TXS 1700+685 as reported by Fermi-LAT collaboration and AGILE team (ATel #14633, ATel #14634).

TXS 1700+685(RA=255.0387208 DE=68.5019331 z=0.301) has been observed by MASTER telescopes at MASTER-Kislovodsk, MASTER-IAC and MASTER-Tavrida several times since the last report on its gamma-ray flare on 2021 March 16(ATel #14463) with no filter.
For unfiltered frames the stars were calibrated by GAIA EDR3’s G magnitude.
On the night from the 16 to 17 March 2021 blazar demonstrates an intranight variability with an amplitude of 0.1-0.2 mag with an average magnitude W=16.30+/-0.03.
From this day blazar was steadily dimming until March 23, when it was detected on W=17.0+/-0.1.
Following this is a gap in observations until May 11 21:20 UTC, when it was detected on W=15.26+/-0.01.
Observations on the next day at 22:29 UTC showed that it dimmed to W=15.43+/-0.02, after which it started rapidly brightening and achieved 15.31+/-0.02 at 22:46 UTC, 15.13+/-0.02 at 00:36 May 13, 14.83+/-0.02 at 02:55 UTC May 13.
On the May 16 20:30 UTC MASTER-Kisl observed the blazar with Jonhson filters V and R.
The stars were calibrated by APASS and PPMX. In V band blazar was detected at 15.55+/-0.03, while in R band it was detected at 15.05+/-0.03 and 15.43+/-0.02 in sequent frames, exposure time was 180s.
There were no hot pixels on the place of the blazar and other stars with similar magnitude don’t show such trend, so the reason for such a sharp jump is likely not connected with our telescope or the condition of atmosphere.

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