Author ORCID Identifier

https://orcid.org/0000-0001-5645-5336

Semester

Fall

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Maura McLaughlin

Committee Member

Loren Anderson

Committee Member

David Kaplan

Committee Member

Duncan Lorimer

Abstract

Last year, pulsar timing arrays (PTAs) reported evidence of a gravitational-wave (GW) background at nanohertz frequencies, opening a new window into the Universe. PTAs measure GW-induced variations in the timing of radio pulses from millisecond pulsars (MSPs) in our Galaxy. In order for PTA experiments to confidently detect and characterize the GW background, they must continue to regularly observe many MSPs and measure their pulse times of arrival as precisely as possible. This motivates efforts to find new MSPs with pulsar surveys, and to study pulsars whose unusual behavior may give rise to excess noise in PTA data sets, potentially reducing sensitivity to GWs. A particularly important assumption of most pulsar timing methods is that the average pulse profile (radio light curve folded on the spin period of the pulsar) is stable with time. We have analyzed pulsar timing observations of 21 pulsars discovered in surveys with the Green Bank Telescope. We present average pulse profiles and timing solutions, and discuss interesting individual sources. We developed a mathematical extension of the ELL1 binary timing model to accommodate PSRs J0032+6946 and J0214+5222, two wide-orbit binaries with low eccentricities. We also show evidence that suggests PSR J1327+3423's dispersion measure is higher towards lower frequencies, a phenomenon predicted by Cordes et al. (2016). Two pulsars in our analysis, PSRs J0636+5128 and J1327+3423, have been observed by PTAs. We also present a study of PSR J1022+1001, an MSP which exhibits unusual pulse profile variability. Using Arecibo observations at 430 MHz, 1.4 GHz, and 2 GHz in the North American Nanohertz Observatory for Gravitational Waves' 15-year data set, we investigated the possibility that this variability is caused by polarization miscalibration. We applied two polarization calibration techniques in tandem: Measurement Equation Modeling and Measurement Equation Template Matching, to fully characterize the polarimetric responses of each receiver over the span of the data set. Presenting calibrated polarimetric profiles, we found these are no less variable than those calibrated with the standard noise-diode polarization calibration commonly used in pulsar timing observations. We favor causes intrinsic to the pulsar itself as the cause of the observed variability.

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