Search for Eccentric Binary Neutron Star Mergers in the first and second observing runs of Advanced LIGO

Alexander H. Nitz^1,2, Amber Lenon³, Duncan A. Brown⁴

<sub>1. Albert-Einstein-Institut, Max-Planck-Institut for Gravitationsphysik, D-30167 Hannover, Germany
2. Leibniz Universitat Hannover, D-30167 Hannover, Germany
3. Department of Physics and Astronomy, West Virginia University, Morgantown WV 26506, USA 4. Department of Physics, Syracuse University, Syracuse, NY 13244, USA</sub>

Introduction

We present a search for gravitational waves from merging binary neutron stars which have non-negligible eccentricity as they enter the LIGO observing band. We use the public Advanced LIGO data which covers the period from 2015 through 2017 and contains $\sim164$ days of LIGO-Hanford and LIGO-Livingston coincident observing time. The search was conducted using matched-filtering using the PyCBC toolkit. We find no significant binary neutron star candidates beyond GW170817, which has previously been reported by searches for binaries in circular orbits. We place a 90 % upper limit of $\sim1700$ mergers $\textrm{Gpc}^{-3} \textrm{Yr}^{-1}$ for eccentricities $\lesssim 0.43$ at a dominant-mode gravitational-wave frequency of 10 Hz. The absence of a detection with these data is consistent with theoretical predictions of eccentric binary neutron star merger rates. Using our measured rate we estimate the sensitive volume of future gravitational-wave detectors and compare this to theoretical rate predictions. We find that, in the absence of a prior detection, the rate limits set by six months of Cosmic Explorer observations would constrain all current plausible models of eccentric binary neutron star formation.

The catalog is stored in the file '1-ECCBNS.hdf'. There are a variety of tools to access hdf files from numerous computing languages. Here we will focus on access through python and h5py.

Analysis Details

Details of the analysis are available in this preprint paper and the configuration files needed to create the analysis workflows are provided in the workflow/configuration directory.

Accessing the Catalog: 1-ECCBNS.hdf

import h5py

catalog = h5py.File('./1-ECCBNS.hdf', 'r')

# Accessing a column by name
ranking_values = catalog['stat'][:]

File format

The file constains a set of named columns. Some of these columns give information specific to either the LIGO Hanford or Livingston detectors. Where this is the case, the name of the column is prefixed with either a H1 or L1.

Key	Description
name	The designation of the candidate event. This is of the form 150812+12:23:04UTC.
far	The rate of false alarms with a ranking statistic as large or larger than this event. The unit is yr^-1.
stat	The value of the ranking statistic for this candidate event.
mass1	The component mass of one compact object in the template waveform which found this candidate. Units in detector frame solar masses.
mass2	The component mass of the template waveform which found this candidate. Units in detector frame solar masses.
eccentricity	The eccentricity parameter of the binary merger
{H1/L1}_end_time	The time in GPS seconds when a fiducial point in the signal passes throught the detector. Typically this is near the time of merger.
{H1/L1}_snr	The amplitude of the complex matched filter signal-to-noise observed.
{H1/L1}_coa_phase	The phase (angle) of the complex matched filter signal-to-noise observed.
{H1/L1}_reduced_chisq	Value of the signal consistency test defined in this paper. This is not calculated for all candidate events. In this case a value of 0 is substituted.
{H1/L1}_sigmasq	The integral of the template waveform divided by the power spectral density.

This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 United States License.

We encourage use of these data in derivative works. If you use the material provided here, please cite the paper using the reference:

@article{,
      key            = "1770186",
      author         = "Nitz, Alexander H. and Lenon, Amber and Brown, Duncan A.",
      title          = "{Search for Eccentric Binary Neutron Star Mergers in the
                        first and second observing runs of Advanced LIGO}",
      year           = "2019",
      eprint         = "1912.05464",
      archivePrefix  = "arXiv",
      primaryClass   = "astro-ph.HE",
      SLACcitation   = "%%CITATION = ARXIV:1912.05464;%%"
}

Acknowledgments

We thank Nico Yunes and Blake Moore for their feedback and guidance using TaylorF2e. DAB thanks National Science Foundation Grant No.~PHY-1707954 for support. AL thanks The Center for Gravitational Waves and Cosmology at West Virginia University, and the Division of Diversity Equity and Inclusion at West Virginia University for support. We acknowledge the Max Planck Gesellschaft for support and the Atlas cluster computing team at AEI Hannover. This research was supported in part by the National Science Foundation under Grant No.~PHY-1748958. This research has made use of data, software and/or web tools obtained from the Gravitational Wave Open Science Center (https://www.gw-openscience.org), a service of LIGO Laboratory, the LIGO Scientific Collaboration and the Virgo Collaboration. LIGO is funded by the U.S. National Science Foundation. Virgo is funded by the French Centre National de Recherche Scientifique (CNRS), the Italian Istituto Nazionale della Fisica Nucleare (INFN) and the Dutch Nikhef, with contributions by Polish and Hungarian institutes.