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MASTER-SAAO: bright dwarf nova outburstsients

ATel #9007; P. Balanutsa, O. Gress, V. Shumkov, S. Shurpakov, V. Lipunov (Lomonosov MSU), D. Buckley (SAAO), V. Kornilov, E. Gorbovskoy, N. Tiurina, A. Kuznetsov, D. Kuvshinov, V. Vladimirov, I. Gorbunov, D. Vlasenko, E. Popova (Lomonosov Moscow State University, SAI), S. Potter, A. Kniazev (The South African Astronomical Observatory)
on 28 Apr 2016; 21:06 UT
Credential Certification: Nataly Tyurina (tiurina@sai.msu.ru)

Subjects: Optical, Request for Observations, Cataclysmic Variable, Transient, Variables

MASTER OT J112814.90-752122.0 - dwarf nova outburt, ampl>4.7

MASTER-SAAO auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L ) discovered OT source at (RA, Dec) = 11h 28m 14.90s -75d 21m 22.0s on 2016-04-27.86791 UT.
The OT unfiltered magnitude is 17.3m (limit 19.3m).
There are 3 images with OT this night. There is its previous outburst on 2014-12-31 23:59:08.467 with m_OT=17.0 (m_OT=17.6 on 2015-01-04 23:54:01.271) in MASTER-SAAO database.
We have reference image without OT on 2015-10-22.10256 UT with unfiltered magnitude limit 19.9m.
There is no any known source in VIZIER database, it means 22 POSs limit and more then 4.7mag current outburst
Spectral observations are required.
The discovery and reference images are available at http://master.sai.msu.ru/static/OT/112814.90-752122.0.png

MASTER OT J185103.43-772041.6 discovery - dwarf nova outburt with ampl>3.7m

MASTER-SAAO auto-detection system discovered OT source at (RA, Dec) = 18h 51m 03.43s -77d 20m 41.6s on 2016-04-27.96184 UT.
The OT unfiltered magnitude is 16.6m (limit 19.4m).
The OT is seen in 5 images. We have previous outburst of this OT on 2015-12-03 19:55:30.362UT with unfiltered m_OT=18.2.
There are reference images without OT in MASTER-SAAO database with the following unfiltered (w=0.2B+0.8R calibrated by USNO-B1) magnitude limits
2016-03-23 23:21:36 UT m_lim=19.0
2016-01-30 01:11:36 UT m_lim=19.5
2014-12-20.02241 UT , m_lim=19.6m
2015-09-09 00:41:23 UT , m_lim=19.4
2015-02-03 01:28:35 UT, m_lim=19.5
2014-12-20 01:06:18 UT m_lim=19.5
There is USNO-B1 star with B2=20.2,R2=20.3, so we suggest the amplitude of current outburst more then 3.7m
20.2120.30 Spectral observations are required. The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/185103.43-772041.6.png

MASTER OT J173801.07-790114.1 discovery - posibly dwarf nova outburt, Ampl>3.3m

MASTER-SAAO auto-detection system discovered OT source at (RA, Dec) = 17h 38m 01.07s -79d 01m 14.1s on 2016-04-27.95955 UT.
The OT unfiltered magnitude is 18.7m (limit 19.4m).
The OT is seen in 3 images. There is no minor planet at this place.
There is no any sources in VIZIER datatabse, that means the 22m POSS limit and current outburst's amlitude more then 3.3m
We have reference image without OT on 2016-03-21.02377 UT with unfiltered magnitude limit 19.5m.
Spectral observations are required.
The discovery and reference images are available at http://master.sai.msu.ru/static/OT/173801.07-790114.1.png

MASTER OT J151830.91-770656.7 discovery - posible dwarf nova outburt with ampl>3.3m

MASTER-SAAO auto-detection system discovered OT source at (RA, Dec) = 15h 18m 30.91s -77d 06m 56.7s on 2016-04-27.93054 UT.
The OT unfiltered magnitude is 18.3m (the limit is 19.4m).
The OT is seen in 3 image on 27.931, 27.938, 27.949UT. Also this OT is seen on 2015-04-14 23:35:26.227UT with m_OT=19.9+-0.2.
We have reference image without OT on 2015-03-01.81338 UT with 18.9 unfiltered magnitude limit 18.9m, on 2015-12-12 00:48:32UT with m_lim=19.9.
There is GSC2.3.2 blue star with known jmag=21.66, so the amplitude of current outburst is more then 3.4m
Spectral observations are required.
The discovery and reference images are available at http://master.sai.msu.ru/static/OT/151830.91-770656.7.png

Current outbursts:
MASTER OT J072351.31+635526.2 (ATEL #4001) with unfiltered m_OT=16.6

MASTER Global Robotic Net