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: name: Coughlin, Michael W.
name: Ahumada, Tomás
name: Anand, Shreya
name: De, Kishalay
name: Hankins, Matthew J.
name: Kasliwal, Mansi M.
name: Singer, Leo P.
name: Bellm, Eric C.
name: Andreoni, Igor
name: Cenko, S. Bradley
name: Cooke, Jeff
name: Copperwheat, Christopher M.
name: Dugas, Alison M.
name: Jencson, Jacob E.
name: Perley, Daniel A.
name: Yu, Po-Chieh
name: Bhalerao, Varun
name: Kumar, Harsh
name: Bloom, Joshua S.
name: Anupama, G. C.
name: Ashley, Michael C. B.
name: Bagdasaryan, Ashot
name: Biswas, Rahul
name: Buckley, David A. H.
name: Burdge, Kevin B.
name: Cook, David O.
name: Cromer, John
name: Cunningham, Virginia
name: D'Aì, Antonino
name: Dekany, Richard G.
name: Delacroix, Alexandre
name: Dichiara, Simone
name: Duev, Dmitry A.
name: Dutta, Anirban
name: Feeney, Michael
name: Frederick, Sara
name: Gatkine, Pradip
name: Ghosh, Shaon
name: Goldstein, Daniel A.
name: Golkhou, V. Zach
name: Goobar, Ariel
name: Graham, Matthew J.
name: Hanayama, Hidekazu
name: Horiuchi, Takashi
name: Hung, Tiara
name: Jha, Saurabh W.
name: Kong, Albert K. H.
name: Giomi, Matteo
name: Kaplan, David L.
name: Karambelkar, V. R.
name: Kowalski, Marek
name: Kulkarni, Shrinivas R.
name: Kupfer, Thomas
name: La Parola, Valentina
name: Masci, Frank J.
name: Mazzali, Paolo
name: Moore, Anna M.
name: Mogotsi, Moses
name: Neill, James D.
name: Ngeow, Chow-Choong
name: Martínez-Palomera, Jorge
name: Pavana, M.
name: Ofek, Eran O.
name: Patil, Atharva Sunil
name: Riddle, Reed
name: Rigault, Mickael
name: Rusholme, Ben
name: Serabyn, Eugene
name: Shupe, David L.
name: Sharma, Yashvi
name: Sollerman, Jesper
name: Soon, Jamie
name: Staats, Kai
name: Taggart, Kirsty
name: Tan, Hanjie
name: Travouillon, Tony
name: Troja, Eleonora
name: Waratkar, Gaurav
name: Yatsu, Yoichi
Publisher: name: arXiv
Year: 2019
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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 deg$^2$ of the initial skymap over the next two nights, corresponding to 46\% integrated probability, ZTF system achieved a depth of $\approx$\,21 $m_\textrm{AB}$ 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 sky map. The revised skymap issued the following day reduced these numbers to 21\% for the Zwicky Transient Facility 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 lightcurves 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.