MASTER: new OT with ampl>5.7m and fast variability

ATel #13747; Yu. P.Sergienko (BSPU), P. Balanutsa, V. Lipunov (Lomonosov MSU), R. Podesta, F. Podesta, C. Francile (OAFA), H. Levato, C. Mallamacci (SJNU), D. A. H. Buckley (SAAO), K. Zhirkov, V. Kornilov, E. Gorbovskoy, O. Gress, A. Chasovnikov, N. Tiurina, P. Balanutsa, I. Gorbunov, A. Kuznetsov, V. Vladimirov, D. Vlasenko, F. Balakin, D. Zimnukhov, D. Cheryasov, V. Senik, E. Minkina, V. Grinshpun, V. Shumkov, T. Pogrosheva, V. Topolev, A. Pozdnyakov (Lomonosov MSU), N. M. Budnev(ISU, API), V. Yurkov, A. Gabovich (BSPU), R. Rebolo, M. Serra-Riscart, (IAC), A. Tlatov, D. Dormidontov(Kislovodsk Solar Station of the Pulkovo Observatory)
on 20 May 2020; 22:44 UT
Credential Certification: Nataly Tyurina (tiurina@sai.msu.ru)

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MASTER OT J195117.88+075920.4 discovery - new OT with ampl>5.7m

AT2020kot
During Fermi trigger 611605955 inspection by MASTER (Lipunov et al. GCN #27762 , https://master.sai.msu.ru/site/master2/observ.php?id=1360824 )
MASTER-SAAO auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L )
discovered OT source at (RA, Dec) = 19h 51m 17.88s +07d 59m 20.4s on 2020-05-20.04965 UT.
The OT unfiltered magnitude is 16.3m at (mlim=19.1, MASTER-SAAO),
also m_OT=16.4 at 2020-05-20 02:19:58UT (MASTER-IAC),
and marginally seen with m <~16.5-17 at 2020-05-20 10:19:54UT (MASTER-OAFA).
We reobserved it at MASTER-Kislovodsk at 2020-05-20 22:00:56UT, that excluded OT from candidates to GRB (36%)counterpart
.But
It has fast decay now (MASTER is twin telescope):
date_UT unfiltered_m_OT
2020-05-20 22:00:56 16.5
2020-05-20 22:00:56 16.5
2020-05-20 22:04:17 16.9
2020-05-20 22:04:17 16.9

We have reference image on 2016-08-11.79161 UT with unfiltered mlim= 19.1m.
There is no any souces inside 4", it gives 22m POSS limit and more then 5.7m of outburst amplitude in the case of CV nature
Spectral observations are required.
The discovery and reference images are available at:
http://master.sai.msu.ru/static/OT/195117.88075920.4.png

MASTER devoted this OT to professor Yuri Pavlovich Sergienko, our member, big friend and comrade from MASTER-Amur (Russian Far East), rector of Blagoveschensk State Pedagogical University, who was died on 17th of May.

MASTER Global Robotic Net