TITLE:   GCN CIRCULAR
NUMBER:  26794
SUBJECT: LIGO/Virgo S200115j: No notable candidates in GOTO imaging
DATE:    20/01/17 00:16:40 GMT
FROM:    Danny Steeghs at U.of Warwick/GOTO  <dsteeghs@gmail.com>

D.Steeghs (1); K.Ulaczyk (1); J.Lyman (1); R.Cutter (1); T.Killestein
(1); M.Dyer (3); M.Kennedy (10); G.Ramsay (5); D.K.Galloway (2);
V.Dhillon (3); P.O'Brien (4); D.Pollacco (1); E.Thrane (2);
S.Poshyachinda (6); S.Mattila (7); L.Nuttall (8); E.Palle (9);
A.Levan (1); T.Marsh (1); R.West (1); E.Stanway (1); B.Gompertz (1);
K.Wiersema (1); ; K.Ackley (2); Y.-L.Mong (2); A.Casey (2); M.Brown
(2); B.Muller (2); J.Mullaney (3); E.Daw (3); S.Littlefair (3);
J.Maund (3); L.Makrygianni (3); R.Starling (4); R.Eyles (4); S.Tooke
(4); S.Aukkaravittayapun (6); U.Sawangwit (6); S.Awiphan (6);
D.Mkrtichian (6); P.Irawati (6); R.Kotak (7); T.Heikkila (7); E.Rol
(2)

(1) Warwick University, (2) Monash University, (3) University of
Sheffield, (4) University of Leicester, (5) Armagh Observatory &
Planetarium, (6) National Astronomical Research Institute of
Thailand, (7) University of Turku, (8) University of Portsmouth, (9)
Instituto de Astrofisica de Canarias), (10) Univ. of Manchester.

report on behalf of the GOTO collaboration:

We report on optical observations with the Gravitational-wave Optical
Transient Observer prototype in response to S200115j (GCN #26759).
Targeted observations started shortly after the preliminary event
notification was received. These spanned 43 distinct tile pointings
containing 59.6% of the source location probability (based on the
initial BAYESTAR skymap) and were acquired between 04:34 UT Jan 15
2019 and 06:55 UT Jan 16 2019 (starting 11 minutes after the event
time).

Each pointing spans 4.9x3.7 square degrees and consisted of 3x60s
exposures in our L-band filter (400-700nm passband similar to g+r)
with a median 5-sigma photometric depth equivalent to g=19.5 for an
individual pointing. Limits are based on a photometric calibration
against PS1 sources. Most pointings were observed multiple times,
typically 2-3 times.

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 following data
acquisition and automated classifier cuts. For a small number of
tiles no suitable reference frames were available, reducing the
searched probability area to 51.7%.

No new transients were detected that could be credibly associated
with S200115j. We did not detect any significant sources at the
location of the reported ZTF candidates (GCN #26767), as expected
given our limiting magnitudes for those exposures.


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), The University
of Portsmouth, the University of Turku and the Instituto de
Astrofisica de Canarias (IAC) (https://goto-observatory.org/)