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Title: A Radio Counterpart to a Neutron Star Merger
Authors:
G. Hallinan
1*‡
, A. Corsi
2‡
, K. P. Mooley
3
, K. Hotokezaka
4,5
, E. Nakar
6
, M.M.
Kasliwal
1
, D.L. Kaplan
7
, D.A. Frail
8
, S.T.
Myers
8
, T. Murphy
9,10
, K. De
1
, D. Dobie
9,10,1
1
, J.R.
Allison
9,12
K.W. Bannister
11
, V. Bhalerao
13
, P. Chandra
14
†, T.E. Clarke
15
, S. Giacintucci
15
,
A.Y.Q. Ho
1
, A. Horesh
16
, N.E. Kassim
15
, S. R. Kulkarni
1
, E. Lenc
9,10
, F.
J. Lockman
17
, C.
Lynch
4,1
0
, D. Nichols
18
, S. Nissanke
18
, N. Palliyaguru
2
, W.M. Peters
9
, T. Piran
12
, J. Rana
19
, E. M.
Sadler
9,10
, L.P. Singer
20
Affiliations:
1
Division of Physics, Mathematics and Astronomy, California Institute of Technology, 1200 East
California Boulevard, Pasadena, CA 91125, USA
2
Department of Physics and Astronomy, Texas Tech University, Box 41051, Lubbock, TX
79409-
1051, USA
3
Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH,U
K
4
Center for Computational Astrophysics, Flatiron Institute, 162 5th Ave, New York, NY 10010,
USA
5
Department of Astrophysical Sciences, Princeton University, P
eyton Hall, Princeton, NJ
08544 USA
6
The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel
Aviv 69978, Israel
7
Department of Physics, University of Wisconsin, Milwaukee, WI 53201, USA
8
National Radio Astronomy Observatory, Socorro, New Mexico, 87801, USA
9
Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006,
Australia
10
Australian
Research Council
Centre of Excellence for All
-sky Astrophysics (CAASTRO)
11
Australia Telescope National Facility
, Commonwealth Scientific and Industrial Research
Organisation, Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
12
Australia
n Research Council
Centre of Excellence for All
-sky Astrophysics in 3 Dimensions
(ASTRO 3D)
13
Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India
14
National
Centre
for Radio Astrophysics, Tata Institu
te of Fundamental Resear
ch, Pune
University
Campus, Ganeshkhind Pune 411007, India
15
Remote Sensing Division, Naval Research Laboratory, Code 7213, 4555 Overlook Ave. S W,
Washington, DC 20375
16
Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel
17
Green Bank Observatory, P.O. Box 2, Green Bank, WV 24944
18
Institute of Mathematics, Astrophysics and Particle Physics, Radboud University,
Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
19
Inter University Centre for Astronomy and Astrophysics (IUCAA), S. P. Pune University
Campus
, Pune, Maharashtra 411007, India
20
Astroparticle Physics Laboratory, NASA Goddard Space Flight Center, Mail Code 661,
Greenbelt, MD
20771, USA
† Current address:
Department of Astronomy, Stockholm University, Alba
Nova, SE
-106 91
Stockholm
* Correspondence to: gh@astro.caltech.edu
‡ These authors contributed equally to this work.
Abstract
: Gravitational waves have been detected from a binary neutron star merger event,
GW170817. The detection of electromagnetic radiation from the same source has shown that the
merger occurred in the outskirts of the galaxy NGC 4993, at a distance of 40 megaparsecs from
Earth. We report the detection of a counterpart radio source that appears 16 days after the event,
allowing us to diagnose the energetics and environment of the merger. The observed radio
emission can be explained by either a collimated ultra-
relativistic jet viewed off
-axis, or a cocoon
of mildly relativistic ejecta. Within 100 days of the merger, the radio light curves will distinguish
between these models and very long baseline interferometry will have the capability to directly
measure the angular velocity and geometry of the debris.
One Sentence Summary:
The radio counterpart of the binary neutron star merger GW170817
probes the energetics and environment of the explosion.
Main text
On 2017 August 17, the A
dvanced Laser Interferometer Grav
itational Wave Observatory
(Advanced LIGO) detected a gravitational wave signal, GW170817, which was rapidly identified
to be associated with the inspiral and coalescence of two neutron stars (
1
). A burst of gamma
-rays,
GRB170817A, was detected approximate
ly two seconds after the gravitational wave detection by
the
Gamma
-ray Burst Monitor (GBM)
of
the Fermi Gamma
-ray Space Telescope
(
2
4
). With the
addition of data from the Advanced Virgo interferometer, the source of gravitational waves was
localized to an area of 28 deg
2
(90% confidence region) and a distance of 40 ± 8 megaparsecs
(Mpc) (
1
). There were 49 cataloged galaxies within this volume, allowing astronomers to rapidly
search for electromagnetic counterparts (5). An optical counterpart, designated S
SS17a, was
detected within ~11 hours of the event by astronomers using the Swope telescope, localizing the
merger to the S0-
type galaxy NGC
4993 at a distance of 40 Mpc
(6,7
)
. It was independently
confirmed soon after (
8,9
). Following the optical detections, targeted observing campaigns were
initiated across the electromagnetic spectrum (
10
). Subsequent optical and infrared spectroscopic
observations firmly established this optical counterpart to be associated with the neutron star
merger GW170817 (
5
).
We report a coordinated effort to use the Karl G. Jansky Very Large Array (VLA), the VLA Low
Band Ionosphere and Transient Experiment (VLITE), the Australia Telescope Compact Array
(ATCA) and the Giant Metrewave Radio Telescope (GMRT) to constrain th
e early time radio
properties of the neutron star merger. Companion papers
report the ultraviolet and X
-ray properties
(
11
) and interpret the panchromatic behavior of the transient (
5
). The multi
-wavelength counterpart
to GW170817 is hereafter referred to as EM170817.
The Search for a Radio Counterpart to GW170817
We began radio observations of NGC 4993 on August 17 2017 at 01:46 UT
C, within ~13 hours of
the detection of the gravitational event. These initial observations were part of a survey with the
ATCA
, targeting
galaxies in the gravitational wave localization region
as identified by the Census
of the Local Universe (
CLU) catalog (
5
) . A similar survey of these
CLU
cataloged galaxies also
commenced with the VLA.
After confirmation of a compelling
optica
l counterpart to the merger,
observations focused on the location of EM170817, with coordination between the VLA, ATCA,
GMRT and VLITE enabling monitoring on a close to dai
ly basis at frequencies spanning 0.3
– 10