TITLE:   GCN CIRCULAR
NUMBER:  24425
SUBJECT: GRB 190507B: GOTO optical counterpart search
DATE:    19/05/08 11:45:34 GMT
FROM:    Danny Steeghs at U.of Warwick/GOTO  <dsteeghs@gmail.com>

Y-L.Mong(1), K.Ackley(1), M.Kennedy(2), A.Obradovic(1), D.K.Galloway(1),
D.Steeghs(3), J.Lyman(3), K.Ulaczyk(3), K.Wiersema(3), M.Dyer(4),
V.Dhillon(4),
P.O'Brien(5), G.Ramsay(6), D.Pollacco(3), E.Thrane(1), S.Poshyachinda(7),
E.Palle(8), R.Cutter(3), A.Levan(3), T. Marsh(3), R.West(3), ,
B.Gompertz(3),
E.Stanway(3),  A.Casey(1), M.Brown(1), E.Rol(1), J.Mullaney(4),
S.Littlefair(4),
L.Makrygianni(4), E.Daw(4), J.Maund(4), R.Starling(5), R.Eyles(5),
S.Tooke(5),
U.Sawangwit(7), D.Mkrtichian(7), S.Awiphan(7), S.Aukkaravittayapun(7),
P.Irawati(7),
R.Breton(2), D.Mata-Sanchez(2), T.Heikkila(9), R.Kotak(9)
(1) Monash University; (2) Univ. of Manchester; (3) Warwick University;
(4) Univ. of Sheffield; (5) University of Leicester; (6) Armagh Observatory;
(7) National Astronomical Research Institute of Thailand;
(8) Instituto de Astrofisica de Canarias; (9) University of Turku

report on behalf of the GOTO collaboration:

We carried out observations with the Gravitational-wave Optical
Transient Observer (GOTO), in response to the Fermi trigger 578963794
(GRB190507.97, on 2019 May 7 23:16:29.64 UT, GCN #24422).

We made a series of 60s observations using our wide L-band filter
(400-700 nm), beginning on 2019 May 8 02:55 UT. We observed five
pointings covering 81.9% of the estimated sky uncertainty region of
3.9 degrees radius (68% confidence based on skymap linked in GCN
#24422).

We found no credible counterparts to the GRB detection, down to a
typical (5-sigma) limit of 19.7 mag.

We identify a single transient candidate, GOTO2019ayff, at
19:14:03.21, -23:12:37.88 detected at 17.66+/-0.03 mag (L) on 2019
May 8, 03:10 UT. The transient was subsequently found in a previous
image of the field on 2019 May 2 04:17:29 UT, pre-dating the Fermi
trigger, and is thus unrelated to the GRB. The estimated magnitude
(based on PS1 g-band calibrators) is roughly consistent with the
C-band limit reported for the Fermi trigger field by the MASTER
network (GCN #24423).

No object is known in Gaia DR2, Pan-STARRS, APASS, 2MASS, SIMBAD, or
TNS within 2.5" of this position. The source is close to (3.5"), but
clearly distinct from, a g=17.7 star in Pan-STARRS DR2 and was not
present in our reference epoch taken on 2019 April 13. The transient
may be associated with the nearby (20") galaxy 2MASX
J19140330-2312186.

GOTO is operated at the La Palma observing facilities of the
University of Warwick on behalf of a consortium including the
University of Warwick, Monash University, Armagh Observatory, the
University of Leicester, the University of Sheffield, the National
Astronomical Research Institute of Thailand (NARIT) and the Instituto
de Astrofisica de Canarias (IAC) (https://goto-observatory.org)