MASTER-SAAO: bright optical transients

ATel #8968; V. Shumkov, T. Pogrosheva, V. Lipunov (Lomonosov MSU), D. Buckley (SAAO), E. Gorbovskoy, N. Tiurina, P. Balanutsa, A. Kuznetsov, V. Kornilov, I. Gorbunov, O. Gress, E. Popova(Lomonosov Moscow State University, SAI), S. Potter A. Kniazev (SAAO)
on 18 Apr 2016; 20:28 UT
Credential Certification: Nataly Tyurina (tiurina@sai.msu.ru)

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MASTER OT J184536.01-470222.5 discovery - bright outburst(possible dwarf nova) with ampl>5.6

MASTER-SAAO auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 349171 ) discovered OT source at (RA, Dec) = 18h 45m 36.01s -47d 02m 22.5s on 2016-04-18.02170 UT.
The OT unfiltered magnitude is 16.4m (limit 18.9m).
The OT is seen in 3 images. There is no minor planet at this place. We have reference image without OT on 2015-03-25.02940 UT with unfiltered magnitude limit 20.1m.
There is no any source in VIZIER database, so the optical amplitude of this outburst is more then 5.6m.
Spectral observations are required.
The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/184536.01-470222.5.png

MASTER OT J153041.15-723208.8 discovery - dwarf nova, Ampl>3m

MASTER-SAAO auto-detection system discovered OT source at (RA, Dec) = 15h 30m 41.15s -72d 32m 08.8s on 2016-04-15.93713 UT.
The OT unfiltered magnitude is 16.6m (limit 19.3m). The OT is seen in 3 images. We also have 3 images with m_OT=17.4 on 2014-12-18 01:51:23.167UT.
We have reference images without OT on the following dates:
2015-06-22.75169 UT with 19.6m unfiltered magnitude limit,
2015-12-29 00:35:37 with m_lim=18.9
2015-12-26 01:32:55 with m_lim=18.2
2015-12-21 01:15:45 with m_lim=18.7
2015-12-16 01:22:00 with m_lim=18.5
2015-10-22 18:14:40 with m_lim=18.8
2015-06-22 18:02:26 with m_lim=19.6
2015-04-26 03:31:26 with m_lim=19.2
2015-03-29 22:09:45 with m_lim=19.1
2015-03-02 22:44:42 with m_lim=19.2
2015-01-12 00:55:16 with m_lim=19.0

There is USNO-B1 star(also previous outburst) with B2=16.6,R1=16.47.
So we suggest the dwarf nova with current outburst Spectral observations are required.
The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/153041.15-723208.8.png

MASTER OT J212126.83-155406.6 discovery - dwarf nova outburst, ampl>4.6

MASTER-SAAO auto-detection system discovered OT source at (RA, Dec) = 21h 21m 26.83s -15d 54m 06.6s on 2016-04-18.09016 UT.
The OT unfiltered magnitude is 17.4m (limit 19.9m).
The OT is seen in 8 images. We have reference image without OT on 2015-03-26.13075 UT with unfiltered magnitude limit 19.4m.
There is no known optical source in VIZIER database(POSS optical limit in 22mag), so the amplitude of outburst is more then 4.6m
Spectral observations are required.
The discovery and reference images are available at:http://master.sai.msu.ru/static/OT/212126.83-155406.6.png

MASTER Global Robotic Net