MASTER bright OT detection during Fermi GBM trigger inspection in SDSS galaxy direction

ATel #11935; O. Gress, V. Lipunov (Lomonosov MSU), D. Buckley(SAAO), R. Podesta, F. Podesta, C. Francile (OAFA), H. Levato (ICATE), E. Gorbovskoy, V. Kornilov, N. Tiurina, P. Balanutsa, A. Kuznetsov, V. Vladimirov, D. Zimnukhov, D. Vlasenko (Lomonosov MoscowState University, SAI)
on 11 Aug 2018; 08:17 UT
Credential Certification: Nataly Tyurina (tiurina@sai.msu.ru)

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MASTER OT J023059.78-172027.1 discovery - OT in far SDSS galaxy direction, discovered during Fermi 555576051 trigger inspection

MASTER-SAAO auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L )
discovered OT source at (RA, Dec) = 02h 30m 59.78s -17d 20m 27.1s on 2018-08-11.15934 UT
The OT unfiltered magnitude is 17.5m (mlim=19.7). The OT is seen in 4 images. There is no minor planet at this place.
We have reference image on 2016-05-28.17676 UT with unfiltered mlim= 18.6m.
This OT was found during Fermi trigger inspection (GRBtime=2018-08-10 06:40:46.74UT), but it was presented in MASTER-OAFA images on 2018-08-08 07:33:12 with m_OT=18.5 (also detected during Fermi inspection, but trigger number is 555263883 https://gcn.gsfc.nasa.gov/other/555263883.fermi )

There is SDSS galaxy (The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy, 2012) with 0.25 arcsec offset (inside our error box ~0.7 arcsec) with r_m = 22.5 mag .

However, we can not exclude that the object in the SDSS is a star. In this case we have an optical transient is CV.

Finally, we just received a telegram from MASTER-OAFA robotic telescope (Argentina), that OT magnitude is about 18.0 (Lipunov et al., GCN 23126 ).
Spectral observations are required.
The discovery and reference images are available at:
http://master.sai.msu.ru/static/OT/023059.78-172027.1.png

MASTER Global Robotic Net