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Fast-transient Searches in Real Time with ZTFReST: Identification of Three Optically Discovered Gamma-Ray Burst Afterglows and New Constraints on the Kilonova Rate

Andreoni, Igor and Coughlin, Michael W. and Kool, Erik C. and Kasliwal, Mansi M. and Kumar, Harsh and Bhalerao, Varun and Carracedo, Ana Sagués and Ho, Anna Y. Q. and Pang, Peter T. H. and Saraogi, Divita and Sharma, Kritti and Shenoy, Vedant and Burns, Eric and Ahumada, Tomás and Anand, Shreya and Singer, Leo P. and Perley, Daniel A. and De, Kishalay and Fremling, U. C. and Bellm, Eric C. and Bulla, Mattia and Crellin-Quick, Arien and Dietrich, Tim and Drake, Andrew and Duev, Dmitry A. and Goobar, Ariel and Graham, Matthew J. and Kaplan, David L. and Kulkarni, S. R. and Laher, Russ R. and Mahabal, Ashish A. and Shupe, David L. and Sollerman, Jesper and Walters, Richard and Yao, Yuhan (2021) Fast-transient Searches in Real Time with ZTFReST: Identification of Three Optically Discovered Gamma-Ray Burst Afterglows and New Constraints on the Kilonova Rate. Astrophysical Journal, 918 (2). Art. No. 63. ISSN 0004-637X. doi:10.3847/1538-4357/ac0bc7.

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The most common way to discover extragalactic fast transients, which fade within a few nights in the optical, is via follow-up of gamma-ray burst and gravitational-wave triggers. However, wide-field surveys have the potential to identify rapidly fading transients independently of such external triggers. The volumetric survey speed of the Zwicky Transient Facility (ZTF) makes it sensitive to objects as faint and fast fading as kilonovae, the optical counterparts to binary neutron star mergers, out to almost 200 Mpc. We introduce an open-source software infrastructure, the ZTF REaltime Search and Triggering, ZTFReST, designed to identify kilonovae and fast transients in ZTF data. Using the ZTF alert stream combined with forced point-spread-function photometry, we have implemented automated candidate ranking based on their photometric evolution and fitting to kilonova models. Automated triggering, with a human in the loop for monitoring, of follow-up systems has also been implemented. In 13 months of science validation, we found several extragalactic fast transients independently of any external trigger, including two supernovae with post-shock cooling emission, two known afterglows with an associated gamma-ray burst (ZTF20abbiixp, ZTF20abwysqy), two known afterglows without any known gamma-ray counterpart (ZTF20aajnksq, ZTF21aaeyldq), and three new fast-declining sources (ZTF20abtxwfx, ZTF20acozryr, ZTF21aagwbjr) that are likely associated with GRB200817A, GRB201103B, and GRB210204A. However, we have not found any objects that appear to be kilonovae. We constrain the rate of GW170817-like kilonovae to R < 900 Gpc⁻³ yr⁻¹ (95% confidence). A framework such as ZTFReST could become a prime tool for kilonova and fast-transient discovery with the Vera Rubin Observatory.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Andreoni, Igor0000-0002-8977-1498
Coughlin, Michael W.0000-0002-8262-2924
Kool, Erik C.0000-0002-7252-3877
Kasliwal, Mansi M.0000-0002-5619-4938
Kumar, Harsh0000-0003-0871-4641
Bhalerao, Varun0000-0002-6112-7609
Carracedo, Ana Sagués0000-0002-3498-2167
Ho, Anna Y. Q.0000-0002-9017-3567
Pang, Peter T. H.0000-0001-7041-3239
Sharma, Kritti0000-0002-4477-3625
Burns, Eric0000-0001-8018-5348
Ahumada, Tomás0000-0002-2184-6430
Anand, Shreya0000-0003-3768-7515
Singer, Leo P.0000-0001-9898-5597
Perley, Daniel A.0000-0001-8472-1996
De, Kishalay0000-0002-8989-0542
Fremling, U. C.0000-0002-4223-103X
Bellm, Eric C.0000-0001-8018-5348
Bulla, Mattia0000-0002-8255-5127
Dietrich, Tim0000-0003-2374-307X
Duev, Dmitry A.0000-0001-5060-8733
Goobar, Ariel0000-0002-4163-4996
Graham, Matthew J.0000-0002-3168-0139
Kaplan, David L.0000-0001-6295-2881
Kulkarni, S. R.0000-0001-5390-8563
Laher, Russ R.0000-0003-2451-5482
Mahabal, Ashish A.0000-0003-2242-0244
Shupe, David L.0000-0003-4401-0430
Sollerman, Jesper0000-0003-1546-6615
Walters, Richard0000-0002-1835-6078
Yao, Yuhan0000-0001-6747-8509
Additional Information:© 2021. The American Astronomical Society. Received 2021 April 15; revised 2021 June 2; accepted 2021 June 12; published 2021 September 8. M.W.C acknowledges support from the National Science Foundation with grant number PHY-2010970. M.B. acknowledges support from the Swedish Research Council (Reg. no. 2020-03330). A.S.C, E.C.K., A.G., and J.S., acknowledge support from the G.R.E.A.T. research environment funded by Vetenskapsrådet, the Swedish Research Council, under project number 2016-06012, and support from The Wenner-Gren Foundations. Bayes factor computations between kilonova and GRB afterglow models have used computational resources provided through SuperMUC_NG (LRZ) under project number pn29ba and Hawk (HLRS) under project number 44189. This work was supported by the GROWTH 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 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-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW. The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant No. 12540303 (PI: Graham). The Liverpool Telescope is 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. This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. The ATLAS project is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queens University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile. Software: Astropy (Astropy Collaboration et al. 2013); CASA (McMullin et al. 2007); HEALPix (Górski et al. 2005); simsurvey (Feindt et al. 2019).
Group:Astronomy Department, Infrared Processing and Analysis Center (IPAC), Zwicky Transient Facility
Funding AgencyGrant Number
Swedish Research Council2020-03330
Swedish Research Council2016-06012
Wenner-Gren FoundationsUNSPECIFIED
ZTF partner institutionsUNSPECIFIED
Heising-Simons Foundation12540303
Science and Technology Facilities Council (STFC)ST/T000198/1
Science and Technology Facilities Council (STFC)ST/S006109/1
Subject Keywords:Transient detection; Transient sources; Optical astronomy; Gamma-ray bursts; Neutron stars
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Transient detection (1957); Transient sources (1851); Optical astronomy (1776); Gamma-ray bursts (629); Neutron stars (1108)
Record Number:CaltechAUTHORS:20210520-150004474
Persistent URL:
Official Citation:Igor Andreoni et al 2021 ApJ 918 63
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109221
Deposited By: George Porter
Deposited On:24 May 2021 17:40
Last Modified:23 Sep 2021 15:22

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