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GCN Circular 21179

Subject
GRB 170531B: MASTER Net optical counterpart refind position and magnitude
Date
2017-06-01T11:21:45Z (7 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
N.Tyurina, V. Lipunov, V.Kornilov, E.Gorbovskoy,  I.Gorbunov, D.Kuvshinov, 
A.V.Krylov, P.Balanutsa, A.Kuznetsov, V.V.Chazov, D. Vlasenko
Lomonosov Moscow State University, Sternberg Astronomical Institut of MSU

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

N.M.Budnev, O.Gres, O. Ershova
Irkutsk State University

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

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

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

R.Podesta, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA),
National University of San Juan, Argentina

H. Levato, C. Saffe
Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE),
San Juan, Argentina


MASTER-Kislovodsk robotic telescope (2x4 square degrees, MASTER-Net: 
http://observ.pereplet.ru)  was pointed to the  GRB170531B (Evans et al.,
GCN #21171)  12 sec after notice time and 452 sec after trigger time on 
2017-05-31 22:09:44 UT (Lipunov et al., GCN #21173).


Id 	    Date      time   Exp  Proc.type     Limit* 	Tube  OT   Err
                        UT    sec                5sigma

1240587  2017-05-31 22:09:44  90 Alert (SWIFT)	 18.3   EAST  18.3  0.5
1240589  2017-05-31 22:11:23 110 Alert (SWIFT)   18.4   EAST  18.4  0.5
1240591  2017-05-31 22:13:24 130 Alert (SWIFT)   18.5   EAST  18.4  0.5
1240593  2017-05-31 22:15:44 160 Alert (SWIFT)   18.5   EAST  18.5  0.5
1240596  2017-05-31 22:18:35 180 Alert (SWIFT)   18.5   EAST  18.5  0.5
1240652  2017-05-31 22:09:44 490 SumAlert(SWIFT) 19.1 	EAST  18.3  0.2 
1240597  2017-05-31 22:21:59 180 Alert (SWIFT) 	 18.3   EAST   no    -
1240599  2017-05-31 22:25:24 180 Alert (SWIFT) 	 18.5   EAST   no    - 
.................................................................
1240629  2017-05-31 23:16:43 180 Alert (SWIFT) 	 18.5   EAST   no    -

* - unfiltered magnitude with respect to USNO B1.0 stars reference stars 
m=0.2B + 0.8R

We refind OT preliminary astrometric position  (Lipunov et al., GCN 
#21173) which was done visually.
Our refind position are:

RA,DEC = 19 07 32.19 -16 25 06.9

3 sigma error = (+/-)2 arcsec (the source is marginaly visible). Our pixel 
is 2 arcsec.

The offset from X-ray Swift position (Osborne at all) is 1.9 arcsec .

The position of the Postigo et al. ( GCN 21177) is inside our error box 
(offset ~ 1.9 arcsec).

The  possible OT position Pozanenko et al.( GCN #21174) offset ~ 8.2 arc 
sec.

The OT detection image is available.

The message may be cited.

====================================================================


The observations made on zenit distance = 64 degrees, galaxy latitude b = -11 
degree.
The moon (44 % bright part) below the horizon (The Moon altitude is -6 degree).
The sun  altitude  is -22.7 degree.
The object can be observed till sunrise at 2017-06-01 01:30:50 .



The message may be cited.
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