4 research outputs found
Search for Post-merger Gravitational Waves from the Remnant of the Binary Neutron Star Merger GW170817
The first observation of a binary neutron star coalescence by the Advanced
LIGO and Advanced Virgo gravitational-wave detectors offers an unprecedented
opportunity to study matter under the most extreme conditions. After such a
merger, a compact remnant is left over whose nature depends primarily on the
masses of the inspiralling objects and on the equation of state of nuclear
matter. This could be either a black hole or a neutron star (NS), with the
latter being either long-lived or too massive for stability implying delayed
collapse to a black hole. Here, we present a search for gravitational waves
from the remnant of the binary neutron star merger GW170817 using data from
Advanced LIGO and Advanced Virgo. We search for short ( s) and
intermediate-duration ( s) signals, which includes
gravitational-wave emission from a hypermassive NS or supramassive NS,
respectively. We find no signal from the post-merger remnant. Our derived
strain upper limits are more than an order of magnitude larger than those
predicted by most models. For short signals, our best upper limit on the
root-sum-square of the gravitational-wave strain emitted from 1--4 kHz is
Hz at 50% detection
efficiency. For intermediate-duration signals, our best upper limit at 50%
detection efficiency is Hz for
a millisecond magnetar model, and
Hz for a bar-mode model. These results indicate that post-merger
emission from a similar event may be detectable when advanced detectors reach
design sensitivity or with next-generation detectors
Directly comparing GW150914 with numerical solutions of Einstein's equations for binary black hole coalescence
We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, including
several performed specifically to reproduce this event. Our calculations go beyond existing semianalytic
models, because for all simulations – including sources with two independent, precessing spins – we perform
comparisons which account for all the spin-weighted quadrupolar modes, and separately which account for all
the quadrupolar and octopolar modes. Consistent with the posterior distributions reported in LVC-PE[1] (at
the 90% credible level), we find the data are compatible with a wide range of nonprecessing and precessing
simulations. Followup simulations performed using previously-estimated binary parameters most resemble the
data, even when all quadrupolar and octopolar modes are included. Comparisons including only the quadrupolar
modes constrain the total redshifted mass Mz ∈ [64M� − 82M�], mass ratio 1/q = m2/m1 ∈ [0.6, 1], and
effective aligned spin χeff ∈ [−0.3, 0.2], where χeff = (S1/m1 + S2/m2) · Lˆ /M. Including both quadrupolar
and octopolar modes, we find the mass ratio is even more tightly constrained. Even accounting for precession,
simulations with extreme mass ratios and effective spins are highly inconsistent with the data, at any mass.
Several nonprecessing and precessing simulations with similar mass ratio and χeff are consistent with the data.
Though correlated, the components’ spins (both in magnitude and directions) are not significantly constrained
by the data: the data is consistent with simulations with component spin magnitudes a1,2 up to at least 0.8, with
random orientations. Further detailed followup calculations are needed to determine if the data contain a weak
imprint from transverse (precessing) spins. For nonprecessing binaries, interpolating between simulations, we
reconstruct a posterior distribution consistent with previous results. The final black hole’s redshifted mass is
consistent with Mf,z
in the range 64.0M� − 73.5M� and the final black hole’s dimensionless spin parameter is
consistent with af = 0.62 − 0.73. As our approach invokes no intermediate approximations to general relativity
and can strongly reject binaries whose radiation is inconsistent with the data, our analysis provides a valuable
complement to LVC-PE[1]
Upper limits on the rates of binary neutron star and neutron star-black hole mergers from advanced LIGO’s first observing run
We report here the non-detection of gravitational waves from the merger of binary–neutron star systems and neutron star–black hole systems during the first observing run of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). In particular, we searched for gravitational-wave signals from binary–neutron star systems with component masses and component dimensionless spins <0.05. We also searched for neutron star–black hole systems with the same neutron star parameters, black hole mass , and no restriction on the black hole spin magnitude. We assess the sensitivity of the two LIGO detectors to these systems and find that they could have detected the merger of binary–neutron star systems with component mass distributions of 1.35 ± 0.13 M ? at a volume-weighted average distance of ~70 Mpc, and for neutron star–black hole systems with neutron star masses of 1.4 M ? and black hole masses of at least 5 M ?, a volume-weighted average distance of at least ~110 Mpc. From this we constrain with 90% confidence the merger rate to be less than 12,600 Gpc?3 yr?1 for binary–neutron star systems and less than 3600 Gpc?3 yr?1 for neutron star–black hole systems. We discuss the astrophysical implications of these results, which we find to be in conflict with only the most optimistic predictions. However, we find that if no detection of neutron star–binary mergers is made in the next two Advanced LIGO and Advanced Virgo observing runs we would place significant constraints on the merger rates. Finally, assuming a rate of Gpc?3 yr?1, short gamma-ray bursts beamed toward the Earth, and assuming that all short gamma-ray bursts have binary–neutron star (neutron star–black hole) progenitors, we can use our 90% confidence rate upper limits to constrain the beaming angle of the gamma-ray burst to be greater than 2\buildrel{\circ}\over{.} {3}_{-1.1}^{+1.7} (4\buildrel{\circ}\over{.} {3}_{-1.9}^{+3.1})
Effects of waveform model systematics on the interpretation of GW150914
Parameter estimates of GW150914 were obtained using Bayesian inference, based on three semi-analytic waveform models for binary black hole coalescences. These waveform models differ from each other in their treatment of black hole spins, and all three models make some simplifying assumptions, notably to neglect sub-dominant waveform harmonic modes and orbital eccentricity. Furthermore, while the models are calibrated to agree with waveforms obtained by full numerical solutions of Einstein's equations, any such calibration is accurate only to some non-zero tolerance and is limited by the accuracy of the underlying phenomenology, availability, quality, and parameter-space coverage of numerical simulations. This paper complements the original analyses of GW150914 with an investigation of the effects of possible systematic errors in the waveform models on estimates of its source parameters. To test for systematic errors we repeat the original Bayesian analysis on mock signals from numerical simulations of a series of binary configurations with parameters similar to those found for GW150914. Overall, we find no evidence for a systematic bias relative to the statistical error of the original parameter recovery of GW150914 due to modeling approximations or modeling inaccuracies. However, parameter biases are found to occur for some configurations disfavored by the data of GW150914: for binaries inclined edge-on to the detector over a small range of choices of polarization angles, and also for eccentricities greater than ~0.05. For signals with higher signal-to-noise ratio than GW150914, or in other regions of the binary parameter space (lower masses, larger mass ratios, or higher spins), we expect that systematic errors in current waveform models may impact gravitational-wave measurements, making more accurate models desirable for future observations