From the Big Bang to Tumbleweeds: Analysis of Signals from Relic Gravitons, Neutron Stars, and Terrestrial Gravitational Noise in Gravitational Wave Detectors

This dissertation explores three separate issues in the field of gravitational-wave astronomy: optimal detection algorithms for quasi-periodic signals, gravitational-wave signatures of the equation of state in the early universe, and local Newtonian gravitational noise from nearby airborne masses as possible contaminants of the gravitational-wave signal. Continuous quasi-periodic signals are waveforms that maintain phase coherence over times longer than practical observation times, although the phase may drift in a way that can be modeled with few parameters. Sensitivity to such signals is limited by the computational cost of the analysis, especially since the detection algorithm must search over many values of the parameters in the phase model; it is therefore crucial to develop computationally efficient search strategies. One such strategy is a hierarchical stack search: a technique combining coherent phase corrections on short stretches of data with incoherent frequency drift corrections among several such stretches. The procedure is repeated at least twice, with each pass increasing the confidence in any putative signal. This dissertation discusses how to choose parameter values and observation times for greatest sensitivity, and shows how several astrophysically interesting sources may be detectable by this method. A background of gravitational waves originating in the Big Bang or a pre-Big-Bang collapsing universe will not thermalize in any cosmological epoch, but may be amplified by an intermediate epoch when the wavelengths were stretched outside the Hubble radius. The present-day spectral index is related simply and generically to the initial spectrum, and to the cosmological equation of state at the beginning and end of the intermediate epoch. This dissertation derives this relation, and compares it to related but more model-specific formulae in the current literature. Finally, this dissertation considers two atmospheric sources of background Newtonian gravita­tional noise (infrasonic pressure waves and wind-advected density perturbations), and two sources of transient Newtonian gravitational signals (atmospheric shockwaves and massive airborne bodies, especially tumbleweeds). Neither background noise source will exceed the noise floor for advanced detectors, but sonic booms and wind-borne debris striking the detector can both produce detectable spurious signals through their gravitational effects. Possible corrective measures arc discussed.</p

Observational Limit on Gravitational Waves from Binary Neutron Stars in the Galaxy

Using optimal matched filtering, we search 25 hours of data from the LIGO 40-m prototype laser interferometric gravitational-wave detector for gravitational-wave chirps emitted by coalescing binary systems within our Galaxy. This is the first test of this filtering technique on real interferometric data. An upper limit on the rate R of neutron star binary inspirals in our Galaxy is obtained: with 90% confidence, R\u3c0.5h−1. Similar experiments with LIGO interferometers will provide constraints on the population of tight binary neutron star systems in the Universe

Pulsar timing and spacetime curvature

We analyze the effect of weak field gravitational waves on the timing of pulsars, with particular attention to gauge invariance, that is, to the effects that are independent of the choice of coordinates. We find (1) the Doppler shift cannot be separated into gauge invariant gravitational wave and kinetic contributions; (2) a gauge invariant separation can be made for the time derivative of the Doppler shift in which the gravitational wave contribution is directly related to the Riemann tensor, and the kinetic contribution is that for special relativity; (3) the gaugedependent effects in the Doppler shift play no role in the program of gravitational wave detection via pulsar timing. The direct connection shown between pulsar timing and the Riemann tensor of the gravitational waves will be of importance in discussions of gravitational waves from alternative (non-Einsteinian) theories of gravitation

Tumbleweeds and airborne gravitational noise sources for LIGO

Gravitational-wave detectors are sensitive not only to astrophysical gravitational waves, but also to the fluctuating Newtonian gravitational forces of moving masses in the ground and air around the detector. This paper studies the gravitational effects of density perturbations in the atmosphere, and from massive airborne objects near the detector. These effects were previously considered by Saulson; in this paper I revisit these phenomena, considering transient atmospheric shocks, and the effects of sound waves or objects colliding with the ground or buildings around the test masses. I also consider temperature perturbations advected past the detector as a source of gravitational noise. I find that the gravitational noise background is below the expected noise floor even of advanced interferometric detectors, although only by an order of magnitude for temperature perturbations carried along turbulent streamlines. I also find that transient shockwaves in the atmosphere could potentially produce large spurious signals, with signal-to-noise ratios in the hundreds in an advanced interferometric detector. These signals could be vetoed by means of acoustic sensors outside of the buildings. Massive wind-borne objects such as tumbleweeds could also produce gravitational signals with signal-to-noise ratios in the hundreds if they collide with the interferometer buildings, so it may be necessary to build fences preventing such objects from approaching within about 30m of the test masses.Comment: 15 pages, 10 PostScript figures, uses REVTeX4.cls and epsfig.st

Strong field effects on pulsar arrival times: Circular orbits and equatorial beams

If a pulsar orbits a supermassive black hole, the timing of pulses that pass close to the hole will show a variety of strong field effects. To compute the intensity and timing of pulses that have passed close to a nonrotating black hole, we introduce here a simple formalism based on two \ universal functions,\ one for the bending of photon trajectories and the other for the photon travel time on these trajectories. We apply this simple formalism to the case of a pulsar in circular orbit that beams its pulses into the orbital plane. In addition to the \ primary\ pulses that reach the receiver by a more-or-less direct path, we find that there are secondary and higher-order pulses. These are usually much dimmer than the primary pulses, but they can be of comparable or even greater intensity if they are emitted when pulsar is on the side of the hole furthest from the receiver. We show that there is a phase relationship of the primary and secondary pulses that is a probe of the strongly curved spacetime geometry. Analogs of these phenomena are expected in more general configurations, in which a pulsar in orbit around a hole emits pulses that are not confined to the orbital plane. © 2009. The American Astronomical Society. All rights reserved

Pulsar timing and the detection of black hole binary systems in globular clusters

The possible existence of intermediate mass binary black holes (IMBBHs) in globular clusters (GCs) offers a unique geometry in which to detect space-time oscillations. For certain pulsar-IMBBH configurations possible within a GC, the usual far-field plane wave approximation for the IMBBH metric perturbation severely underestimates the magnitude of the induced pulsar pulse time-of-arrival (TOA) fluctuations. In this letter, the expected TOA fluctuations induced by an IMBBH lying close to the line-of-sight between a pulsar and the Earth are calculated for the first time. For an IMBBH consisting of 10 Msolar and 10^3 Msolar components, a 10 year orbital period, and located 0.1 lyr from the Earth-Pulsar line of sight, the induced pulsar timing residual amplitude will be of order 5 to 500 ns.Comment: Accepted into ApJ Letters. This is a slightly augmented version containing one extra figur

Detection of pulsar beams deflected by the black hole in Sgr A*: effects of black hole spin

Some Galactic models predict a significant population of radio pulsars close to the our galactic center. Beams from these pulsars could get strongly deflected by the supermassive black hole (SMBH) believed to reside at the galactic center and reach the Earth. Earlier work assuming a Schwarzschild SMBH gave marginal chances of observing this exotic phenomenon with current telescopes and good chances with future telescopes. Here we calculate the odds of observability for a rotating SMBH. We find that the estimates of observation are not affected by the SMBH spin, but a pulsar timing analysis of deflected pulses might be able to provide an estimate of the spin of the central black hole.Comment: 15 pages aastex, 8 Fig

Search for Gravitational Waves Associated with Fast Radio Bursts Detected by CHIME/FRB During the LIGO–Virgo Observing Run O3a

We search for gravitational-wave transients associated with fast radio bursts (FRBs) detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project (CHIME/FRB), during the first part of the third observing run of Advanced LIGO and Advanced Virgo (1 April 2019 15:00 UTC–1 Oct 2019 15:00 UTC). Triggers from 22 FRBs were analyzed with a search that targets compact binary coalescences with at least one neutron star component. A targeted search for generic gravitational-wave transients was conducted on 40 FRBs. We find no significant evidence for a gravitational-wave association in either search. Given the large uncertainties in the distances of the FRBs inferred from the dispersion measures in our sample, however, this does not conclusively exclude any progenitor models that include emission of a gravitational wave of the types searched for from any of these FRB events. We report 90% confidence lower bounds on the distance to each FRB for a range of gravitational-wave progenitor models. By combining the inferred maximum distance information for each FRB with the sensitivity of the gravitational-wave searches, we set upper limits on the energy emitted through gravitational waves for a range of emission scenarios. We find values of order 1051–1057 erg for a range of different emission models with central gravitational wave frequencies in the range 70–3560Hz. Finally, we also found no significant coincident detection of gravitational waves with the repeater, FRB20200120E, which is the closest known extragalactic FRB

GW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact Object

We report the observation of a compact binary coalescence involving a 22.2 - 24.3 M⊙ black hole and a compact object with a mass of 2.50 - 2.67 M⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal, GW190814, was observed during LIGO\u27s and Virgo\u27s third observing run on August 14, 2019 at 21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg2 at a distance of 241+41−45 Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal mass ratio yet measured with gravitational waves, 0.112+0.008−0.009, and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to ≤0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1-23 Gpc−3 yr−1 for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of mass ratio, component masses, and the inferred merger rate for this event challenges all current models for the formation and mass distribution of compact-object binaries