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Published July 1, 2018 | Published + Submitted
Journal Article Open

An Upper Limit on the Linear Polarization Fraction of the GW170817 Radio Continuum


We present late-time radio observations of GW170817, the first binary neutron-star (NS) merger discovered through gravitational waves (GWs) by the advanced Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo detectors. Our observations, carried out with the Karl G. Jansky Very Large Array (VLA), were optimized to detect polarized radio emission, and thus to constrain the linear polarization fraction of GW170817. At an epoch of ≈244 days after the merger, we rule out linearly polarized emission above a fraction of ≈12% at a frequency of 2.8 GHz (99% confidence). Within the structured jet scenario (a.k.a. successful jet plus cocoon system) for GW170817, the derived upper limit on the radio continuum linear polarization fraction strongly constrains the magnetic field configuration in the shocked ejecta. We show that our results for GW170817 are compatible with the low level of linear polarization found in afterglows of cosmological long γ-ray bursts (GRBs). Finally, we discuss our findings in the context of future expectations for the study of radio counterparts of binary NS mergers identified by ground-based GW detectors.

Additional Information

© 2018. The American Astronomical Society. Received 2018 June 8; accepted 2018 June 19; published 2018 July 3. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We thank the VLA director's office and schedsoc for approving and promptly executing the observations presented in this study. A.C. and D.C. acknowledge support from the National Science Foundation (NSF) CAREER award #1455090. A.C. thanks Drew Medlin and Jose Salcido for helpful discussions on the VLA automated calibration pipeline, and on polarization calibration in CASA. A.C. is grateful to Roger Blandford for suggesting to carry out radio polarization observations of GW170817 in the radio. A.C. also acknowledges participation in the GROWTH (Global Relay of Observatories Watching Transients Happen) project (National Science Foundation PIRE grant No. 1545949). D.K. was additionally supported by NSF grant AST-1412421. D.L. acknowledges support form the NASA ATP grant NNX17AK42G. K.P.M. is currently a Jansky Fellow of the National Radio Astronomy Observatory.

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Published - Corsi_2018_ApJL_861_L10.pdf

Submitted - 1806.03136


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August 21, 2023
October 18, 2023