CaltechAUTHORS
Published May 20, 2020 | Version Submitted + Published
Journal Article Open

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

Creators

  • 1. ROR icon California Institute of Technology
  • 2. ROR icon Liverpool John Moores University
  • 3. ROR icon National Centre for Radio Astrophysics
  • 4. ROR icon University of Washington
  • 5. ROR icon University of Minnesota
  • 6. ROR icon Ioffe Institute
  • 7. ROR icon Infrared Processing and Analysis Center
  • 8. ROR icon Hebrew University of Jerusalem
  • 9. ROR icon Northwestern University
  • 10. ROR icon Adler Planetarium
  • 11. ROR icon Lawrence Berkeley National Laboratory
  • 12. ROR icon Weizmann Institute of Science

Abstract

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.

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 (ssl.berkeley.edu/ipn3/masterli.html) 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.

Attached Files

Published - Ho_2020_ApJ_895_49.pdf

Submitted - 2003.01222.pdf

Files

2003.01222.pdf

Files (5.8 MB)

Name Size Download all
md5:09b22e79792c7af76f9a195e686611a4
3.2 MB Preview Download
md5:c86a8dc6f39becdd0ac857b9a6ec7640
2.6 MB Preview Download

Additional details

Identifiers

Eprint ID
101783
Resolver ID
CaltechAUTHORS:20200309-115301856

Related works

Describes
https://arxiv.org/abs/2003.01222 (URL)

Funding

NSF Graduate Research Fellowship
DGE-1144469
NSF
OISE-1545949
Heising-Simons Foundation
Department of Science and Technology (India)
DST/SJF/PSA-01/2014-15
Israel Science Foundation
Binational Science Foundation (USA-Israel)
I-CORE Program of the Planning and Budgeting Committee
Gordon and Betty Moore Foundation
GBMF5076
Large Synoptic Survey Telescope Corporation
Brinson Foundation
Northwestern University
NSF
AST-1440341
Caltech
Infrared Processing and Analysis Center (IPAC)
Weizmann Institute of Science
Stockholm University
University of Maryland
University of Washington
Deutsches Elektronen-Synchrotron
Humboldt University
Los Alamos National Laboratory
TANGO Consortium
University of Wisconsin-Milwaukee
Lawrence Berkeley National Laboratory
W. M. Keck Foundation

Dates

Created
2020-03-09
Created from EPrint's datestamp field
Updated
2021-11-16
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
Astronomy Department, Zwicky Transient Facility, Infrared Processing and Analysis Center (IPAC), Division of Geological and Planetary Sciences (GPS)