GCN Circular 23048

V. Lipunov, E. Gorbovskoy, N.Tiurina, D.Vlasenko, V.Kornilov, A.Kuznetsov, 
V.Chazov, I.  Gorbunov, D.Zimnukhov, D.Kuvshinov, P.Balanutsa,
V.Vladimirov,
Lomonosov Moscow State University,SAI

D. Buckley,
South African Astronomical Observatory (SAAO)

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias (IAC)

A. Tlatov, V.Senik, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory

R. Podesta, F. Podesta, C. Lopez, C.Francile
Observatorio Astronomico Felix Aguilar (OAFA)

H.Levato,
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

O. Gres, N.M.Budnev , Yu.Ishmuhametova
Irkutsk State University (ISU)

A. Gabovich, V. Yurkov, Yu. Sergienko
Blagoveschensk Educational State University (BSPU)

MASTER-SAAO robotic telescope (MASTER-Net: http://observ.pereplet.ru, 
Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in 
South Africa (South African Astronomical Observatory) was pointed to the 
GRB180728A 22 sec after notice time and 38 sec after trigger time at 
2018-07-28 17:29:38 UT in two polarizations. On our first (10s exposure) 
set we  found  new optical object (transient) within SWIFT error-box 
(ra=253.567 dec=-54.0308  r=0.05) :

MASTER OT J165415.75 -540239.27
RA, DEC = 16h 54m 15.75s , -54d 02m 39.27s
m ~ 14.5

We  see a surprising automatic light curve  when the source has 
risen to constant magnitude during first ~30 minutes!

The observations made on zenit distance = 28 degrees, galaxy latitude b = 
-7 degree.
The moon (99 % bright part) is 11 degrees above the horizon. The distance 
between  moon and  object is 61
The sun  altitude  is -19.8 degree.
The object can be observed till 2018-07-29 05:17:09

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