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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, D. A. and Kulkarni, S. R. and Andreoni, I. and Bellm, E. C. and Burdge, K. B. and Chandra, P. and Coughlin, M. W. and De, K. and Dong, D. Z. J. and Golkhou, V. Z. and Graham, M. J. and Fredericks, D. D. and Helou, G. and Horesh, A. and Laher, R. R. and Masci, F. and Ridnaia, A. and Rusholme, B. and Shupe, D. L. and Svinkin, D. S. (2020) The Koala: A Fast Blue Optical Transient with Luminous Radio Emission from a Starburst Dwarf Galaxy at z=0.27. . (Submitted)

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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. This event has a number of features in common with the groundbreaking transient AT2018cow: blue colors at peak (g−r ≈ −0.5), a short rise time from half-max of under two days, a decay time of only three days, a high optical luminosity (M_(g,peak) ≈ −20.8), a hot (≳ 40,000K) featureless spectrum at peak light, and a luminous radio counterpart (νL_ν ≳ 10⁴⁰ erg sec⁻¹ at 10 GHz). The radio luminosity of ZTF18abvkwla exceeds that of AT2018cow by an order of magnitude, and the late-time (Δt ≳ 80 days) light curve resembles that of long-duration gamma-ray bursts (GRBs). The host galaxy is a dwarf starburst galaxy (M ≈ 5 × 10⁸ M_⊙, SFR ≈ 7 M_⊙ year⁻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 collimated ejecta 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, 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 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, and prospects for detecting accompanying X-ray and radio emission.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Ho, Anna Y. Q.0000-0002-9017-3567
Perley, D. A.0000-0001-8472-1996
Kulkarni, S. R.0000-0001-5390-8563
Andreoni, I.0000-0002-8977-1498
Bellm, E. C.0000-0001-8018-5348
Burdge, K. B.0000-0002-7226-836X
Coughlin, M. W.0000-0002-8262-2924
De, K.0000-0002-8989-0542
Graham, M. J.0000-0002-3168-0139
Helou, G.0000-0003-3367-3415
Horesh, A.0000-0002-5936-1156
Laher, R. R.0000-0003-2451-5482
Masci, F.0000-0002-8532-9395
Rusholme, B.0000-0001-7648-4142
Shupe, D. L.0000-0003-4401-0430
Additional Information:A.Y.Q.H. is supported by a National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144469. This work was supported by the GROWTH project funded by the National Science Foundation under PIRE Grant No. 1545949. 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.Y.Q.H would like to thank 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 her visit to Socorro when this work was performed. She 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 light curve of SN 2011kl, Miika Pursiainen for sharing light curves of DES fast-luminous transients, Jesper Sollerman for carefully reading the manuscript, and Tony Piro and Ben Margalit for other helpful discussions. This work made use of the IPN master burst list ( maintained by Kevin Hurley.
Group:Astronomy Department, Zwicky Transient Facility, Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1144469
Heising-Simons FoundationUNSPECIFIED
Gordon and Betty Moore Foundation5076
Record Number:CaltechAUTHORS:20200309-115301856
Persistent URL:
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:09 Mar 2020 20:57

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