Effect of eccentricity on binary neutron star searches in advanced LIGO

Binary neutron stars (BNSs) are the primary source of gravitational waves for the Laser Interferometer Gravitational-Wave Observatory (LIGO) and its international partners Virgo and KAGRA. Current BNS searches target field binaries whose orbits will have circularized by radiation reaction before their gravitational waves enter the advanced LIGO sensitive band at 15 Hz. It has been suggested that a population of BNSs may form by $n$-body interactions near supermassive black holes or in globular clusters and that these systems may have non-negligible eccentricity in the advanced LIGO band. We show that for BNS systems with total mass of $2.4M_{\odot }$ ($6M_{\odot }$), the effect of eccentricity $e\lesssim 0.02$ (0.05) is negligible and a circular search is effectual for these binaries. For eccentricities up to $e=0.4$, we investigate the selection bias caused by neglecting eccentricity in BNS searches. If such high eccentricity systems exist, searches that specifically target eccentric binaries will be needed in advanced LIGO and Virgo.

Figure 1

The left panel is a cumulative histogram which indicates the fraction of points in the mass-space region where the bank of noneccentric waveforms has a value of $\mathcal{F}\mathcal{F}$ less than the associated value on the $x$ axis. The right panel shows the $\mathcal{F}\mathcal{F}$ as a function of the binary system’s initial value of eccentricity.

Figure 2

The left panel shows the $\mathcal{F}\mathcal{F}$ as a function of the initial value of the eccentricity and the anomaly of the trajectory for binaries with component masses $1M_{\odot }<m<3M_{\odot }$. The right panel shows the correlation of the $\mathcal{F}\mathcal{F}$ with the initial orbital eccentricity and the total mass of the binary.