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The Koala: A Fast Blue Optical Transient with Luminous Radio Emission from a Starburst Dwarf Galaxy at z = 0.27

Ho, Anna Y. Q. and Perley, Daniel A. and Kulkarni, S. R. and Dong, Dillon Z. J. and De, Kishalay and Chandra, Poonam and Andreoni, Igor and Bellm, Eric C. and Burdge, Kevin B. and Coughlin, Michael and Dekany, Richard and Feeney, Michael and Fredericks, Dmitry D. and Fremling, Christoffer and Golkhou, V. Zach and Graham, Matthew J. and Hale, David and Helou, George and Horesh, Assaf and Kasliwal, Mansi M. and Laher, Russ R. and Masci, Frank J. and Miller, A. A. and Porter, Michael and Ridnaia, Anna and Rusholme, Ben and Shupe, David L. and Soumagnac, Maayane T. and Svinkin, Dmitry S. (2020) The Koala: A Fast Blue Optical Transient with Luminous Radio Emission from a Starburst Dwarf Galaxy at z = 0.27. Astrophysical Journal, 895 (1). Art. No. 49. ISSN 1538-4357.

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We present ZTF18abvkwla (the "Koala"), a fast blue optical transient discovered in the Zwicky Transient Facility (ZTF) One-Day Cadence (1DC) Survey. ZTF18abvkwla has a number of features in common with the groundbreaking transient AT 2018cow: blue colors at peak (g – r ≈ −0.5 mag), a short rise time from half-max of under two days, a decay time to half-max of only three days, a high optical luminosity (M_(g,peak) ≈ −20.6 mag), a hot (≳40,000 K) featureless spectrum at peak light, and a luminous radio counterpart. At late times (Δt > 80 days), the radio luminosity of ZTF18abvkwla (ν_(Lν) ≳ 10⁴⁰ erg⁻¹ at 10 GHz, observer-frame) is most similar to that of long-duration gamma-ray bursts (GRBs). The host galaxy is a dwarf starburst galaxy (M ≈ 5×10⁸ M⊙, SFR ≈ 7 M⊙ yr⁻¹) that is moderately metal-enriched (log[O/H] ≈ 8.5), similar to the hosts of GRBs and superluminous supernovae. As in AT2018cow, the radio and optical emission in ZTF18abvkwla likely arise from two separate components: the radio from fast-moving ejecta (Γβc > 0.38c) and the optical from shock-interaction with confined dense material (<0.07 M⊙ in ∼10¹⁵ cm). Compiling transients in the literature with t_(rise) < 5 days and M_(peak) < −20 mag, we find that a significant number are engine-powered, and suggest that the high peak optical luminosity is directly related to the presence of this engine. From 18 months of the 1DC survey, we find that transients in this rise-luminosity phase space are at least two to three orders of magnitude less common than CC SNe. Finally, we discuss strategies for identifying such events with future facilities like the Large Synoptic Survey Telescope, as well as prospects for detecting accompanying X-ray and radio emission.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ho, Anna Y. Q.0000-0002-9017-3567
Perley, Daniel A.0000-0001-8472-1996
Kulkarni, S. R.0000-0001-5390-8563
De, Kishalay0000-0002-8989-0542
Chandra, Poonam0000-0002-0844-6563
Andreoni, Igor0000-0002-8977-1498
Bellm, Eric C.0000-0001-8018-5348
Burdge, Kevin B.0000-0002-7226-836X
Coughlin, Michael0000-0002-8262-2924
Dekany, Richard0000-0002-5884-7867
Fredericks, Dmitry D.0000-0002-1153-6340
Fremling, Christoffer0000-0002-4223-103X
Golkhou, V. Zach0000-0001-8205-2506
Graham, Matthew J.0000-0002-3168-0139
Helou, George0000-0003-3367-3415
Horesh, Assaf0000-0002-5936-1156
Kasliwal, Mansi M.0000-0002-5619-4938
Laher, Russ R.0000-0003-2451-5482
Masci, Frank J.0000-0002-8532-9395
Miller, A. A.0000-0001-9515-478X
Rusholme, Ben0000-0001-7648-4142
Shupe, David L.0000-0003-4401-0430
Soumagnac, Maayane T.0000-0001-6753-1488
Svinkin, Dmitry S.0000-0002-2208-2196
Additional Information:© 2020 The American Astronomical Society. Received 2020 March 2; revised 2020 April 19; accepted 2020 April 20; published 2020 May 26. A.Y.Q.H thanks the NRAO staff for their help with data calibration and imaging, particularly Steve Myers, Aaron Lawson, Drew Medlin, and Emmanuel Momjian. She is grateful for their support and hospitality during her visit to Socorro. She also thanks Gregg Hallinan and Brad Cenko for their advice on reducing the radio and X-ray data, respectively, Jochen Greiner and Iair Arcavi for their assistance in obtaining the afterglow-subtracted light curve of SN 2011kl, Miika Pursiainen for sharing light curves of DES fast luminous transients, Griffin Hosseinzadeh for useful discussions about iPTF15ul, Jesper Sollerman and Steve Schulze for carefully reading the manuscript, and Tony Piro and Ben Margalit for other productive conversations. This work made use of the IPN master burst list ( maintained by Kevin Hurley. We thank Raffaella Margutti for pointing out a typo in an earlier version of this paper, and the anonymous referee for detailed comments that greatly improved the flow and clarity of the paper. A.Y.Q.H. acknowledges the support of a National Science Foundation Graduate Research Fellowship under grant No. DGE-1144469, the GROWTH project funded by the National Science Foundation under PIRE grant No. 1545949, and the Heising-Simons Foundation. P.C. acknowledges support from the Department of Science and Technology via SwarnaJayanti Fellowship awards (DST/SJF/PSA-01/2014-15). A.H. is grateful for the support by grants from the Israel Science Foundation, the US-Israel Binational Science Foundation, and the I-CORE Program of the Planning and Budgeting Committee and the Israel Science Foundation. This research was funded in part by a grant from the Heising-Simons Foundation and a grant from the Gordon and Betty Moore Foundation through grant GBMF5076, and benefited from interactions with Daniel Kasen and David Khatami, also funded by that grant. A.A.M. is funded by the Large Synoptic Survey Telescope Corporation, the Brinson Foundation, and the Moore Foundation in support of the LSSTC Data Science Fellowship Program; he also receives support as a CIERA Fellow by the CIERA Postdoctoral Fellowship Program (Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University). 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. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We thank the staff of the GMRT that made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Keck:I (LRIS) - , Hale (DBSP) - , EVLA - , GMRT. - Software: Astropy (Astropy Collaboration et al. 2013, 2018), IPython (Pérez & Granger 2007), matplotlib (Hunter 2007), numpy (Oliphant 2006), scipy (Virtanen et al. 2019), extinction (Barbary 2016), LPipe (Perley 2019), PYRAF-DBSP (Bellm & Sesar 2016), IDLAstro.
Group:Astronomy Department, Zwicky Transient Facility, Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1144469
Heising-Simons FoundationUNSPECIFIED
Department of Science and Technology (India)DST/SJF/PSA-01/2014-15
Israel Science FoundationUNSPECIFIED
Binational Science Foundation (USA-Israel)UNSPECIFIED
I-CORE Program of the Planning and Budgeting CommitteeUNSPECIFIED
Gordon and Betty Moore FoundationGBMF5076
Large Synoptic Survey Telescope CorporationUNSPECIFIED
Brinson FoundationUNSPECIFIED
Northwestern UniversityUNSPECIFIED
Infrared Processing and Analysis Center (IPAC)UNSPECIFIED
Weizmann Institute of ScienceUNSPECIFIED
Stockholm UniversityUNSPECIFIED
University of MarylandUNSPECIFIED
University of WashingtonUNSPECIFIED
Deutsches Elektronen-SynchrotronUNSPECIFIED
Humboldt UniversityUNSPECIFIED
Los Alamos National LaboratoryUNSPECIFIED
University of Wisconsin-MilwaukeeUNSPECIFIED
Lawrence Berkeley National LaboratoryUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:Radio transient sources ; High energy astrophysics ; Supernovae ; Core-collapse supernovae ; Jets ; Sky surveys
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Radio transient sources (2008); High energy astrophysics (739); Supernovae (1668); Core-collapse supernovae (304); Jets (870); Sky surveys (1464)
Record Number:CaltechAUTHORS:20200309-115301856
Persistent URL:
Official Citation:Anna Y. Q. Ho et al 2020 ApJ 895 49
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101783
Deposited By: Joy Painter
Deposited On:09 Mar 2020 20:57
Last Modified:26 May 2020 17:55

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