Prospects for Joint Gravitational-Wave and Electromagnetic Observations of Neutron-Star-Black-Hole Coalescing Binaries

Abstract

Coalescing neutron-star-black-hole (NS-BH) binaries are a promising source of gravitational-wave (GW) signals detectable with large-scale laser interferometers such as Advanced Laser Interferometer Gravitational-Wave Observatory and Virgo. They are also one of the main short gamma-ray burst (SGRB) progenitor candidates. If the BH tidally disrupts its companion, an SGRB may be ignited when a sufficiently massive accretion disk forms around the remnant BH. Detecting an NS-BH coalescence both in the GW and electromagnetic (EM) spectrum offers a wealth of information about the nature of the source. How much can actually be inferred from a joint detection is unclear, however, as a mass/spin degeneracy may reduce the GW measurement accuracy. To shed light on this problem and on the potential of joint EM+GW observations, we here combine recent semi-analytical predictions for the remnant disk mass with estimates of the parameter-space portion that is selected by a GW detection. We identify cases in which an SGRB ignition is supported, others in which it can be excluded, and finally others in which the outcome depends on the chosen model for the currently unknown NS equation of state. We pinpoint a range of systems that would allow us to place lower bounds on the equation of state stiffness if both the GW emission and its EM counterpart are observed. The methods we develop can broaden the scope of existing GW detection and parameter-estimation algorithms and could allow us to disregard about half of the templates in an NS-BH search following an SGRB trigger, increasing its speed and sensitivity.

Accuracy and precision of gravitational-wave models of inspiraling neutron star-black hole binaries with spin: Comparison with matter-free numerical relativity in the low-frequency regime

“…Of all the models considered, we find that SEOBNRv2 surpasses others in faithfulness. Using the accuracy measures proposed in [51], we also found SEOBNRv2 to be indistinguishable from true waveforms up to SNRs ≈8 − 14 (16)(17)(18) for aligned (antialigned) BH spins. We therefore recommend that SEOBNRv2 be used in aLIGO parameter estimation efforts for aligned-spin NSBH detection candidates, but we also recommend that SEOBNR be tested for higher component spins.…”

“…The observation and characterization of a population of NSBH sources will also shed light on stellar evolution and compact-binary formation mechanisms: e.g., a gap in the mass distribution of NSs and BHs could shed light on the mechanism of supernova explosions [14][15][16]. An unambiguous detection of GWs from a NSBH system accompanied by electromagnetic observations could provide information about the internal structure of NSs [17] and could provide strong evidence linking compact binary mergers and short gamma-ray bursts (SGRBs) [18][19][20][21]. However, unlocking the full scientific potential of GWs emitted by NSBH coalescences requires both detecting as many such signals as possible and accurately characterizing them to understand the properties of their source binaries.…”

Upper Limits on the Rates of Binary Neutron Star and Neutron Star–black Hole Mergers From Advanced Ligo’s First Observing Run

“…Such systems are most likely to have an EM counterpart, which would be powered by the material from a disrupted NS. These sets of waveform filters were constructed using methods described in Brown et al (2012), Harry et al (2014), and Pannarale & Ohme (2014 Figure 1). In GstLAL, component spins were limited to χ i <0.05 for m i <2.8 M e and χ i <1 otherwise, for mbta χ i <0.05 for m i <2 M e and χ i <1 otherwise.…”

“…In GstLAL, component spins were limited to χ i <0.05 for m i <2.8 M e and χ i <1 otherwise, for mbta χ i <0.05 for m i <2 M e and χ i <1 otherwise. GstLAL also chose to limit the template bank to include only systems for which it is possible for an NS to have disrupted during the late inspiral using constraints described in Pannarale & Ohme (2014). For the mbta search the waveform filters were modeled using the "TaylorT4" time-domain, postNewtonian inspiral approximant ).…”

Neutron Star–Black Hole Coalescence Rate Inferred from Macronova Observations

“…Moreover, the tidal disruption of the NSs in the NS−BH coalescences is necessary for generating electromagnetic (EM) transient emissions like GRBs, otherwise the NSs would have been wholly swallowed by the BHs. The probability of tidal disruption depends * Electronic address: yiming.hu@aei.mpg.de † Electronic address: yzfan@pmo.ac.cn on the mass ratio (η) between the BH and NS, the equation of state (EOS) of the NS material, the initial dimensionless spin (χ) of the BH, and the initial tilt angle of the binary system [6,13,14]. All of these factors make the estimate of NS−BH merger rate from direct observations of sGRB more uncertain.…”