[vsnet-grb-info 22125] LIGO/Virgo S190425z: GOTO observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24224
SUBJECT: LIGO/Virgo S190425z: GOTO observations
DATE:    19/04/26 15:01:12 GMT
FROM:    Danny Steeghs at U.of Warwick/GOTO  <dsteeghs at gmail.com>

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.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 the BNS event S190425z (GCN #24168).

Targeted observations across 136 pointings containing 29.6% of the
source location probability across 2,134 sqr. degrees (based on the
initial BAYESTAR skymap) were performed between 20:38 UT Apr 25 and
05:33 UT Apr 26 2019.

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=20.1, based on a photometric
calibration against PS1 sources. A coverage map is available at
http://goto-observatory.warwick.ac.uk/S190425z.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.

We recover a number of known/already reported transients and variable
objects, but no new candidates were detected that could be credibly
associated with S190425z.

Our coverage includes some of the PS1 candidates (Smith et al. GCN
#24210), but we did not cover the position of AT2019ebq/PS19qp, which
remains an object of interest (Jonker et al. GCN #24221 ; Coughlin et
al. GCN #24223).

We also reviewed the locations of the marginal ATLAS candidates
reported in McBrien et al. (GCN #24197), but detect no sources at
these locations, in line with Perley et al. (GCN #24202). The 5-sigma
limits are provided below.

Name       | IAU Name   | Obs. MJD | Image lim mag (L band 5sig)
ATLAS19hxm |  AT2019dzv | 58598.96 | 20.08
ATLAS19hyx |  AT2019ebl | 58599.03 | 20.63
ATLAS19hyo |  AT2019eao | 58598.93 | 20.50
ATLAS19hwn |  AT2019ebm | 58598.89 | 20.65
ATLAS19hwh |  AT2019ebn | 58598.96 | 20.67


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/)