GCN Circular 24116

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

report on behalf of the GOTO collaboration:

We report on optical observations with the Gravitational-wave Optical
Transient Observer in response to S190412m (GCN #24098).  Targeted
observations across 18 pointings containing 94% of the source
location probability (based on the initial BAYESTAR skymap) were
performed  between 20:28 UT and 22:48 UT Apr 12 2019.

No new transients were detected that could be credibly associated with
S190412m, in line with searches reported in Lipunov et al. (GCN #24099)
and Weiland et al. (GCN #24107).

Each pointing spans 4.9x3.7 square degrees and consisted of 3x60s
exposures in ourL-band filter (400-700nm passband) with a  typical
5-sigma photometric depth equivalent to g=19.4, based on a photometric
calibration against PS1 sources. All pointings were observed twice.

Images are processed immediately after acquisition using the GOTOphoto
pipeline. Difference imaging was performed on the median of each
triplet of exposures using recent survey observations of the same
pointings. Source candidates were initially filtered using a classifier and
cross-matched against a variety of catalogs, including the MPC and PS1.
Human candidate vetting was performed during data acquisition and
processing in case of notable detections.

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/)