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 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/)