{
  "bibcode": "2019GCN.25654....1A",
  "body": "K.Ackley(2), D.Mata-Sanchez(8), Y-L.Mong(2), R.Cutter(1),\nK.Ulaczyk(1), J.Lyman(1), D.Steeghs(1), G.Ramsay(5),\nD.Galloway(2), L.Makrygianni(3), M.Kennedy(8), A.Obradovic(2),\nM.Dyer(3), V.Dhillon(3), P.O'Brien(4), D.Pollacco(1),\nE.Thrane(2), S.Poshyachinda(6), E.Palle(7), K.Wiersema(1),\nT. Marsh(1), R.West(1), B.Gompertz(1), E.Stanway(1),\nA.Casey(2), M.Brown(2), E.Rol(2), J.Mullaney(3), S.Littlefair(3),\nE.Daw(3), J.Maund(3), R.Starling(4), R.Eyles(4), S.Tooke(4),\nU.Sawangwit(6), D.Mkrtichian(6), S.Awiphan(6), S.Aukkaravittayapun(6),\nP.Irawati(6), R.Breton(8), T.Heikkila(9),\nR.Kotak(9), L.Nuttall (10)\n\n(1) Warwick University; (2) Monash University; (3) Univ. of Sheffield;\n(4) University of Leicester; (5) Armagh Observatory & Planetarium;\n(6) National Astronomical Research Institute of Thailand;\n(7) Instituto de Astrofisica de Canarias; (8) Univ. of Manchester;\n(9) University of Turku; (10) University of Portsmouth\n\n\nreport on behalf of the GOTO collaboration:\n\nWe report on observations with the Gravitational-wave Optical\nTransient Observer (GOTO) on La Palma, Canary Islands, in response to\nthe LIGO/Virgo gravitational wave event  S190901ap, triggered\n2019-09-01 23:31:01.838 UTC (GCN #25606).   We performed a series of\n3x60s exposures using a wide (400-700nm passband) L-band filter with a\ntypical 5-sigma photometric depth equivalent to g~20 based on a\nphotometric calibration against PS1 sources.\n\nObservations commenced on 2019-09-01 23:37:46 UT (6.7 min\npost-trigger) and continued  through 2019-09-04 05:45:10 UT. In total\nwe covered 2507 square degrees containing ~28.2% of the total source\nlocation probability (based on the skymap at\nhttps://gracedb.ligo.org/api/superevents/S190901ap/files/bayestar.fits\n.gz) across 162 tiles. The median number of visits per tile was 3,\nwith some tiles visited up to 18 times.\n\nImages are processed immediately after acquisition using the GOTOphoto\npipeline. Difference imaging was performed on the median of each\ntriplet of exposures using recent survey observations of the same\npointings, which were available for 88% of our tiles. Source\ncandidates were initially filtered using a trained classifier and\ncross-matched against a variety of catalogs, including the MPC and\nPS1. Human candidate vetting was performed on those candidates\nidentified by the classifier. No additional viable optical counterpart\ncandidates beyond those already reported were identified.\n\nWe detected AT2019pjv (Lipunov et al. GCN #25649) as a rising\ntransient. The source rose above our detection limit on Sept 2nd, with\ninternal designation GOTO2019hope, and no source was detected at this\nposition during a series of observations preceding the GW event (most\nrecent visit pre-trigger 2019-08-06). We provide the following\npreliminary magnitudes:\n\nDATE:   MAG:\n\n2019-08-06.9    >20\n2019-09-01.9    > 20\n2019-09-02.9    ~ 19.6\n2019-09-03.9    19.0\n\n=======\nGOTO is operated at the La Palma observing facilities of the\nUniversity of Warwick on behalf of a consortium including the\nUniversity of Warwick, Monash University, Armagh Observatory, the\nUniversity of Leicester, the University of Sheffield, the National\nAstronomical Research Institute of Thailand (NARIT) and the Instituto\nde Astrofisica de Canarias (IAC) (https://goto-observatory.org)",
  "circularId": 25654,
  "createdOn": 1567604374000,
  "email": "dsteeghs@gmail.com",
  "subject": "LIGO/Virgo S190901ap: GOTO optical coverage and detection of AT2019pjv",
  "submitter": "Danny Steeghs at U.of Warwick/GOTO  <dsteeghs@gmail.com>",
  "eventId": "LIGO/Virgo S190901ap"
}