TITLE:   GCN CIRCULAR
NUMBER:  24291
SUBJECT: LIGO/Virgo S190426c: GOTO optical coverage - no notable counterparts
DATE:    19/04/27 16:20:13 GMT
FROM:    Danny Steeghs at U.of Warwick/GOTO  <dsteeghs@gmail.com>

D.Steeghs(1), J.Lyman(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.Palle(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), A.Obradovic(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), D.Mata-Sanchez(8),
T.Heikkila(9), R.Kotak(9)
(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) Univ. of Manchester;
(9) University of Turku

report on behalf of the GOTO collaboration:

We report on optical observations with the Gravitational-wave Optical
Transient Observer in response to event S190426c (GCN #24237).

Targeted observations across 49 pointings containing 54.1% of the
source location probability across 755 sqr. degrees (based on the
updated LALInference skymap, GCN #24279) were performed between 20:38
UT Apr 26 and 05:32 UT Apr 27 2019.

A small number of fields were affected by having limited quality
survey reference frames available and the area includes dense low
galactic latitude fields. We recover a number of known/already reported
transients and many foreground variable objects, but no significant
detections of new candidates that could be credibly associated with
S190426c.

Each pointing spans 4.9x3.7 square degrees and consisted of 3x60s
exposures in our L-band filter (400-700nm passband) with typical
5-sigma photometric depth of g=19.9, based on a photometric
calibration against PS1 sources. A coverage map is available at
http://goto-observatory.warwick.ac.uk/S190426c.html

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/)