MASTER-SAAO Detection of an Optical Transient with the Fast Variability

ATel #6976; O. Gress (Irkutsk State University), V. Lipunov, E. Gorbovskoy, N. Tiurina, P. Balanutsa, D. Denisenko, A. Kuznetsov, M. Pruzhinskaya, A. Rufanov, V. Vladimirov, V. G. Kornilov (Lomonosov Moscow State University, SAI), D. Buckley, S. Potter, A. Kniazev, M. Kotze (South African Astronomical Observatory), K. Ivanov, S. Yazev, N. Budnev, V. Poleshchuk, E. Konstantinov (Irkutsk State University), A. Parkhomenko, A. Tlatov, D. Dormidontov, V. Senik (Kislovodsk Solar Station of Pulkovo Observatory RAS), V. Yurkov, Y. Sergienko, D. Varda, E. Sinyakov, A. Gabovich (Blagoveshchensk Educational University), V. Krushinsky, I. Zalozhnih, A. Popov, A. Bourdanov (Ural Federal University), V. Shumkov, S. Shurpakov (MASTER team members)
on 21 Jan 2015; 23:04 UT
Credential Certification: Nataly Tyurina (tiurina@sai.msu.ru)

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MASTER OT J235652.57-580509.1 - possible new short-period CV

MASTER-SAAO auto-detection system (Lipunov et al., 2010, Advances in Astronomy, article id. 349171, pp. 1-7) discovered OT source at (RA, Dec) = 23h 56m 52.57s -58d 05m 09.1s on 2015-01-21.83502 UT. The OT unfiltered magnitude is 17.5m (limit 19.5m). We have reference image without OT on 2014-12-28.87374 UT with unfiltered magnitude limit 19.4m.

The OT is showing rapid variability on MASTER-SAAO images (60-sec exposures) having brightened by ~1.5m in 6 minutes:

Obs.Date (exp.start) Magn.+/-err. 
--------------------------------- 
2015-01-21 19:56:23  19.26+/-0.25 
2015-01-21 20:02:26  17.51+/-0.12 
2015-01-21 20:08:48  17.25+/-0.09

The object has a quiescent UV counterpart GALEX J235652.7-580509 (FUV=22.16+/-0.39 NUV=21.27+/-0.14). It was in outburst on 1975-11-01 blue DSS plate, but not visible on the red and infrared plates. Color-combined DSS finder chart is uploaded to http://master.sai.msu.ru/static/OT/J235652-580509-JRIR.jpg (10'x10' FOV). There is an infrared counterpart AllWISE J235652.67-580509.3 (W1=16.36+/-0.05 W2=16.33+/-0.13). Nothing is present at this position in 1RXS, 2MASS, GCVS and AAVSO VSX. There are two past outbursts in Siding Spring Survey orphan catalog: on 2005-09-02 to 18.2-18.5m and on 2010-11-12 to 17.1-17.5m.

Based on the past outbursts, UV counterpart and amplitude of variability, MASTER OT J235652.57-580509.1 is a possible new cataclysmic variable, likely with a very short orbital period. Follow up observations are required. The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/235652.57-580509.1.png

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