Author ORCID Identifier

https://orcid.org/0000-0002-3654-980X

Semester

Summer

Date of Graduation

2023

Document Type

Thesis

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Maura McLaughlin

Committee Member

Sarah Burke-Spolaor

Committee Member

Duncan Lorimer

Committee Member

Kevin Bandura

Abstract

Pulsars are among the most exotic objects in our Universe. These rapidly
spinning, high magnetic field neutron stars can be used for a wide range of
scientific studies: from the makeup of their own extremely dense and poorly
understood interior to using their extremely regular signals to detect gravita-
tional waves (GWs). Pulsar timing continues to expand to broader communi-
ties, with larger and more sensitive radio telescopes planned and partnerships
between pulsar timing arrays (PTAs) that span the entire globe. A realm of
new physics with the detection of a background hum of gravitational waves
from black holes merging from across the Universe is close at hand. This is
truly the age of pulsar timing for low-frequency GW astrophysics.
With this work, we seek to expand the current techniques of pulsar timing
to the bright future which makes use of Bayesian statistical techniques by more
tightly integrating pulsar timing model fits into the current PTA GW analysis
methodology. We examine four binary millisecond pulsars, PSRs J1640+2224,
J2043+1711, J1600–3053, and J0740+6620, using our generalized Bayesian
pulsar timing methods and find consistency with and often improvement upon
published parameter constraints estimated by general least-squares timing
methods. Our new pulsar masses constraints (medians and 68% confidence
intervals) for our fully general Bayesian timing models are mp = 1.6±1 M⊙ for
J2043+1711 and mp = 2.3+0.9−0.7 M⊙ for J1600–3053, both using the NANOGrav
12.5-yr data release, and mp = 2.06 ± 6 M⊙ for J0740+6620 using the data
from Fonseca et al. (2021).
We then assess the sensitivity of current and future GW detectors to in-
piralling binary black holes (BBHs). We developed the tool, gwent, for cal-
culating detector sensitivities in the three primary GW detector regimes of
ground-based, space-based, and PTA GW observatories. We calculate realis-
tic signal-to-noise ratios using multi-parameter GW source models and find
regions of overlap between ground and space-based observatories as well as
space-based detectors and PTAs for non-spinning, equal mass ratio binaries.
We finally use realistic simulated PTA data to assess the detectablil-
ity of multiple GW backgrounds (GWBs) simultaneously. We simulate two
GWBs, one from supermassive binary black holes (SMBBHs) with spectrum
of γ = 13/3, and a GWB from primordial gravitational waves (PGWs) with a
spectrum of γ = 5 that has half the energy density at a frequency of f = 1/yr
as the SMBBH GWB. We find that the weaker, steeper PGW GWB shows
evidence for separability from the stronger, shallower SMBBH GWB after 17
years of data. With 20 years of data, we can constrain the injected underlying
PGW GWB spectral index and amplitude to 64% and 110%, respectively. We
use our findings and methods to outline a basic protocol to search for multiple
backgrounds in future PTA datasets.

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