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
Date
2019
Authors
Coughlin, Michael W
Ahumada, Tomas
De, Kishalay
Kasliwal, M M
Bellm, Eric C.
Andreoni, Igor
Cenko, S Bradley
Cooke, Jeff
Copperwheat, Chris M.
Dugas, Alison M.
Journal Title
Journal ISSN
Volume Title
Publisher
Institute of Physics Publishing Ltd.
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 mAB 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 GattiniIR. 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.
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Keywords
Gravitational wave astronomy, Transient detection, Optical telescopes
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Source
Astrophysical Journal Letters
Type
Journal article
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Open Access
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