TITLE:   GCN CIRCULAR
NUMBER:  25654
SUBJECT: LIGO/Virgo S190901ap: GOTO optical coverage and detection of AT2019pjv
DATE:    19/09/04 13:39:34 GMT
FROM:    Danny Steeghs at U.of Warwick/GOTO  <dsteeghs@gmail.com>

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

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


report on behalf of the GOTO collaboration:

We report on observations with the Gravitational-wave Optical
Transient Observer (GOTO) on La Palma, Canary Islands, in response to
the LIGO/Virgo gravitational wave event  S190901ap, triggered
2019-09-01 23:31:01.838 UTC (GCN #25606).   We performed a series of
3x60s exposures using a wide (400-700nm passband) L-band filter with a
typical 5-sigma photometric depth equivalent to g~20 based on a
photometric calibration against PS1 sources.

Observations commenced on 2019-09-01 23:37:46 UT (6.7 min
post-trigger) and continued  through 2019-09-04 05:45:10 UT. In total
we covered 2507 square degrees containing ~28.2% of the total source
location probability (based on the skymap at
https://gracedb.ligo.org/api/superevents/S190901ap/files/bayestar.fits
.gz) across 162 tiles. The median number of visits per tile was 3,
with some tiles visited up to 18 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, which were available for 88% of our tiles. Source
candidates were initially filtered using a trained classifier and
cross-matched against a variety of catalogs, including the MPC and
PS1. Human candidate vetting was performed on those candidates
identified by the classifier. No additional viable optical counterpart
candidates beyond those already reported were identified.

We detected AT2019pjv (Lipunov et al. GCN #25649) as a rising
transient. The source rose above our detection limit on Sept 2nd, with
internal designation GOTO2019hope, and no source was detected at this
position during a series of observations preceding the GW event (most
recent visit pre-trigger 2019-08-06). We provide the following
preliminary magnitudes:

DATE:   MAG:

2019-08-06.9    >20
2019-09-01.9    > 20
2019-09-02.9    ~ 19.6
2019-09-03.9    19.0

=======
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)