GCN Circular 17838

E. Gorbovskoy, V. Lipunov,  N.Tyurina, V.Kornilov, P.Balanutsa, 
A.Kuznetsov,D.Kuvshinov,
Lomonosov Moscow State University, Sternberg Astronomical Institute

D.Buckley, S. Potter, A.Kniazev, M.Kotze
South African Astronomical Observatory

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

K.Ivanov, O.Gres, N.M.Budnev, S.Yazev, O.Chuvalaev, 
V.A.Poleshchuk
Irkutsk State University

V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov, A.Gabovich
Blagoveschensk Educational State University, Blagoveschensk

V.Krushinski, I.Zalozhnih,  A. Popov
Ural Federal University, Kourovka

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

Claudio Mallamaci, Carlos Lopez and Federico Podest
Observatorio Astronomico Felix Aguilar (OAFA)

MASTER-Kislovodsk  robotic telescope (MASTER-Net: http://observ.pereplet.ru, 
FOV = 2x2 square degrees in paralel mode ( Lipunov et al., 2010, MASTER 
Robotic Net, Advances in Astronomy, vol. 2010, pp. 1-7)) located in 
Kislovodsk was pointed to the  MAXI/GSC GRB150518A 
(Kawamuro et al., GCN 17825
Not found
 
 
) 21 sec after notice time and 3189 sec after 
trigger time at 2015-05-18 22:35:43 UT. On our first (180s exposure) 
image we do not  found OTs within Swift/XRT  erro-box  (Sbarufatti et al., 
GCN 17827
Not found
 
 
)  brighter then 18.5 .

But we see bright object at positon:  15h 36m 53.67s , +16d 19m  36s.5
with 17.5  unfiltered mag  outside XRT and inside MAXI.


MASTER-SAAO  robotic telescope (MASTER-Net: http://observ.pereplet.ru,
FOV = 2x2 square degrees in paralel mode ( Lipunov et al., 2010, MASTER
Robotic Net, Advances in Astronomy, vol. 2010, pp. 1-7)) located in
Souht Africa Astronomical Observatory was pointed to the  MAXI/GSC 
GRB150518A
(Kawamuro et al., GCN 17825
Not found
 
 
) 13 sec after notice time and 3189 sec after
trigger time at 2015-05-18 22:35:35 UT. On our first (180s exposure)
image we not  found OTs within Swift/XRT error-box (Sbarufatti et al., 
GCN 17827
Not found
 
 
)  brighter then
17.1 .

But we see bright object at positon:  15h 36m 51.70s , +16d 19m  13s.6
with ~ 17.0  unfiltered mag  outside Swift/XRT and inside MAXI.

  There is one asteroid MPC 2010 KL61 with poorly
astrometrical efemerids (Leave for survey recovery) at MPC Data Base.
The offset both Russian and South Africa OT positiion 36 arc sec. This 
corresponds to parallax effect for Solar System Body.

We do not see any OT at the aftergow canditate position (Xu et al.,
GCNC 17829, 17832; Mao et al., GCNC 17830; Littlejohns et al., GCNC 17831;
Moskvitin GCN 17834
Not found
 
 
) with same limit (3 sigma).

We have only one alert image in each telescope because MASTER telescope 
recieved new MAXI correction of the error box and X-ray Transient leave 
the MASTER FOV during alert observations.

But we have observation this X-ray aftergrow position before last 
trigger activated by previouse Fermi (trigger number 451674501, 25 apr 
2015) and during regular synoptic survey (MASTER-Tunka,  ~ 2 days after 
trigger).

Preliminary results:

Id     Pro.type	   Date        time    Exp.time	Limit	Filt.	Site
                               Starting         (3sigma)

759597  SumSurvey 2015-05-20  17:02:11	480	20.1	W	Tunka
1458076 MaxiAlert 2015-05-18  22:35:35 	180 	17.1 	P/ 	SAAO
1458345	MaxiAlert 2015-05-18  22:35:43	180	18.5	P|   Kislovodsk
823020  FermiInsp 2015-04-25  20:11:41 	180 	19.9 	W    Kislovodsk

Where W - unfiltered, P - polarization unfiltered. All magnitude 
calculated with respect to hundrends USNO B stars  with calibration:
  m = 0.2B + 0.8R .


At the Tunka Survey we see marginaly faint (~2 sigma) object on the X-ray 
position (Sbarufatti et al., GCN 17827
Not found
 
 
). But this is may be noice. We have 
a lot of images in MASTER NET Data Base imaging last 
several years with   Swift XRT error box. No object we see on this place 
with 20.5 mag limit on first overview (since 2010).

The message may be cited.