GROWTH on S190425z: Searching Thousands of Square Degrees to Identify an Optical or Infrared Counterpart to a Binary Neutron Star Merger with the Zwicky Transient Facility and Palomar Gattini-IR

Creators: Coughlin, Michael W.; Ahumada, Tomás; Anand, Shreya; De, Kishalay; Hankins, Matthew J.; Kasliwal, Mansi M.; Singer, Leo P.; Bellm, Eric C.; Andreoni, Igor; Cenko, S. Bradley; Cooke, Jeff; Copperwheat, Christopher M.; Dugas, Alison M.; Jencson, Jacob E.; Perley, Daniel A.; Yu, Po-Chieh; Bhalerao, Varun; Kumar, Harsh; Bloom, Joshua S.; Anupama, G. C.; Ashley, Michael C. B.; Bagdasaryan, Ashot; Biswas, Rahul; Buckley, David A. H.; Burdge, Kevin B.; Cook, David O.; Cromer, John; Cunningham, Virginia; D'Aì, Antonino; Dekany, Richard G.; Delacroix, Alexandre; Dichiara, Simone; Duev, Dmitry A.; Dutta, Anirban; Feeney, Michael; Frederick, Sara; Gatkine, Pradip; Ghosh, Shaon; Goldstein, Daniel A.; Golkhou, V. Zach; Goobar, Ariel; Graham, Matthew J.; Hanayama, Hidekazu; Horiuchi, Takashi; Hung, Tiara; Jha, Saurabh W.; Kong, Albert K. H.; Giomi, Matteo; Kaplan, David L.; Karambelkar, V. R.; Kowalski, Marek; Kulkarni, Shrinivas R.; Kupfer, Thomas; Masci, Frank J.; Mazzali, Paolo; Moore, Anna M.; Mogotsi, Moses; Neill, James D.; Ngeow, Chow-Choong; Martínez-Palomera, Jorge; La Parola, Valentina; Pavana, M.; Ofek, Eran O.; Patil, Atharva Sunil; Riddle, Reed; Rigault, Mickael; Rusholme, Ben; Serabyn, Eugene; Shupe, David L.; Sharma, Yashvi; Singh, Avinash; Sollerman, Jesper; Soon, Jamie; Staats, Kai; Taggart, Kirsty; Tan, Hanjie; Travouillon, Tony; Troja, Eleonora; Waratkar, Gaurav; Yatsu, Yoichi

Abstract

The third observing run by LVC has brought the discovery of many compact binary coalescences. Following the detection of the first binary neutron star merger in this run (LIGO/Virgo S190425z), we performed a dedicated follow-up campaign with the Zwicky Transient Facility (ZTF) and Palomar Gattini-IR telescopes. The initial skymap of this single-detector gravitational wave (GW) trigger spanned most of the sky observable from Palomar Observatory. Covering 8000 deg² of the initial skymap over the next two nights, corresponding to 46% integrated probability, ZTF system achieved a depth of ≈21 m_(AB) in g- and r-bands. Palomar Gattini-IR covered 2200 square degrees in J-band to a depth of 15.5 mag, including 32% integrated probability based on the initial skymap. The revised skymap issued the following day reduced these numbers to 21% for the ZTF and 19% for Palomar Gattini-IR. We narrowed 338,646 ZTF transient "alerts" over the first two nights of observations to 15 candidate counterparts. Two candidates, ZTF19aarykkb and ZTF19aarzaod, were particularly compelling given that their location, distance, and age were consistent with the GW event, and their early optical light curves were photometrically consistent with that of kilonovae. These two candidates were spectroscopically classified as young core-collapse supernovae. The remaining candidates were ruled out as supernovae. Palomar Gattini-IR did not identify any viable candidates with multiple detections only after merger time. We demonstrate that even with single-detector GW events localized to thousands of square degrees, systematic kilonova discovery is feasible.

Additional Information

© 2019 The American Astronomical Society. Received 2019 July 29; revised 2019 September 24; accepted 2019 October 4; published 2019 October 30. This work was supported by the GROWTH (Global Relay of Observatories Watching Transients Happen) project funded by the National Science Foundation under PIRE grant No. 1545949. GROWTH is a collaborative project among California Institute of Technology (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK) and University of Sydney (Australia). Based on observations made with the Liverpool Telescope operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The 0.7 m GROWTH-India Telescope (GIT) is set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with support from the Indo-US Science and Technology Forum (IUSSTF) and the Science and Engineering Research Board (SERB) of the Department of Science and Technology (DST), Government of India grant No. IUSSTF/PIRE Program/GROWTH/2015-16. It is located at the Indian Astronomical Observatory, IIA at Hanle, Ladakh (India). This publication has made use of data collected at Lulin Observatory, partly supported by MoST grant 105-2112-M-008-024-MY3. The KPED team thanks the National Science Foundation and the National Optical Astronomical Observatory for making the Kitt Peak 2.1 m telescope available. We thank the observatory staff at Kitt Peak for their efforts to assist Robo-AO KP operations. The KPED team thanks the National Science Foundation, the National Optical Astronomical Observatory, the Caltech Space Innovation Council, and the Murty family for support in the building and operation of KPED. SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171. The Palomar Gattini-IR project thanks the Mount Cuba Foundation, Heising-Simons Foundation, the ANU Futures Scheme, the Binational Science Foundation. and Caltech for generous support. G.C.A. and V.B. acknowledge partial support from SERB and IUSSTF. J.S. acknowledges support from the Knut and Alice Wallenberg Foundation. E.O. is grateful for support by a grant from the Israeli Ministry of Science, ISF, Minerva, BSF, BSF transformative program, and the I-CORE Program of the Planning and Budgeting Committee and The Israel Science Foundation (grant No. 1829/12). P.G. is supported by NASA Earth and Space Science Fellowship (ASTRO18F-0085). C.-C.N., A.P., and P.-C.Y. thank the funding from Ministry of Science and Technology (Taiwan) under grants 104-2923-M-008-004-MY5, 106-2112-M-008-007, 107-2119-M-008-012, 107-2119-M-008-014-MY2 E.B. and V.Z.G. acknowledge support from the University of Washington College of Arts and Sciences, Department of Astronomy, and the DIRAC Institute. University of Washington's DIRAC Institute is supported through generous gifts from the Charles and Lisa Simonyi Fund for Arts and Sciences, and the Washington Research Foundation. E.B. acknowledges support from the Large Synoptic Survey Telescope, which is supported in part by the National Science Foundation through Cooperative Agreement 1258333 managed by the Association of Universities for Research in Astronomy (AURA), and the Department of Energy under Contract No. DE-AC02-76SF00515 with the SLAC National Accelerator Laboratory. Additional LSST funding comes from private donations, grants to universities, and in-kind support from LSSTC Institutional Members. E.B. is supported in part by the NSF AAG grant 1812779 and grant #2018-0908 from the Heising-Simons Foundation. M.W.C. is supported by the David and Ellen Lee Postdoctoral Fellowship at the California Institute of Technology. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. D.L.K. was supported by NSF grant AST-1816492. A.K.H.K. acknowledges support from the Ministry of Science and Technology of the Republic of China (Taiwan) under grants 106-2628-M-007-005 and 107-2628-M-007-003. J.S.B. and J.M.-P. are partially supported by a Gordon and Betty Moore Foundation Data-Driven Discovery grant. H.K. thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant #1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. S.A. acknowledges support from the PMA Division Medberry Fellowship at the California Institute of Technology. R.B., A.G., and J.S. acknowledge support from the G.R.E.A.T research environment funded by the Swedish National Science Foundation. J.S. acknowledges support by an Australian Government Research Training Program (RTP) Scholarship. M.R. acknowledges support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 759194 - USNAC).

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