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Continued Radio Observations of GW170817 3.5 yr Post-merger

Balasubramanian, Arvind and Corsi, Alessandra and Mooley, Kunal P. and Brightman, Murray and Hallinan, Gregg and Hotokezaka, Kenta and Kaplan, David L. and Lazzati, Davide and Murphy, Eric J. (2021) Continued Radio Observations of GW170817 3.5 yr Post-merger. Astrophysical Journal Letters, 914 (1). Art. No. L20. ISSN 2041-8213.

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We present new radio observations of the binary neutron star merger GW170817 carried out with the Karl G. Jansky Very large Array (VLA) more than 3 yr after the merger. Our combined data set is derived by coadding more than ≈32 hr of VLA time on-source, and as such provides the deepest combined observation (rms sensitivity ≈0.99 μJy) of the GW170817 field obtained to date at 3 GHz. We find no evidence for a late-time radio rebrightening at a mean epoch of t ≈ 1200 days since merger, in contrast to a ≈2.1σ excess observed at X-ray wavelengths at the same mean epoch. Our measurements agree with expectations from the post-peak decay of the radio afterglow of the GW170817 structured jet. Using these results, we constrain the parameter space of models that predict a late-time radio rebrightening possibly arising from the high-velocity tail of the GW170817 kilonova ejecta, which would dominate the radio and X-ray emission years after the merger (once the structured jet afterglow fades below detection level). Our results point to a steep energy-speed distribution of the kilonova ejecta (with energy-velocity power-law index α ≳ 5). We suggest possible implications of our radio analysis, when combined with the recent tentative evidence for a late-time rebrightening in the X-rays, and highlight the need for continued radio-to-X-ray monitoring to test different scenarios.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Balasubramanian, Arvind0000-0003-0477-7645
Corsi, Alessandra0000-0001-8104-3536
Mooley, Kunal P.0000-0002-2557-5180
Brightman, Murray0000-0002-8147-2602
Hallinan, Gregg0000-0002-7083-4049
Hotokezaka, Kenta0000-0002-2502-3730
Kaplan, David L.0000-0001-6295-2881
Lazzati, Davide0000-0002-9190-662X
Murphy, Eric J.0000-0001-7089-7325
Additional Information:© 2021. The American Astronomical Society. Received 2021 March 7; revised 2021 April 21; accepted 2021 April 30; published 2021 June 10. We are grateful to Dale A. Frail for contributing to shaping this work with many insightful discussions. A.B. and A.C. acknowledge support from the National Science Foundation via Award #1907975. K.P.M. and G.H. acknowledge support from the National Science Foundation grant AST-1911199. D.L.K. was supported by NSF grant AST-1816492. D.L. acknowledges support from the National Science Foundation via Award #1907955. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Group:Astronomy Department
Funding AgencyGrant Number
Subject Keywords:Radio continuum emission; Radio transient sources; X-ray transient sources
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Radio continuum emission (1340); Radio transient sources (2008); X-ray transient sources (1852)
Record Number:CaltechAUTHORS:20210520-150028754
Persistent URL:
Official Citation:Arvind Balasubramanian et al 2021 ApJL 914 L20
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109229
Deposited By: George Porter
Deposited On:24 May 2021 14:19
Last Modified:10 Jun 2021 20:43

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