Semester

Fall

Date of Graduation

2018

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Maura McLaughlin

Committee Co-Chair

James M. Cordes

Committee Member

James M. Cordes

Committee Member

Sarah Burke-Spolaor

Committee Member

Kathryn Williamson

Abstract

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has the principal goal of detecting gravitational waves (GWs) in the nanohertz part of the spectrum using pulsar timing. This thesis presents results from radio campaigns at frequencies from 322 MHz to 10 GHz aimed at both multi-messenger constraints on GW sources and improving the timing sensitivity. The primary expected source of GWs at the nanohertz frequencies to which pulsar timing is sensitive are supermassive black hole (SMBH) binaries. We investigate a purported SMBH displaced from the galactic photocenter in NGC 3115. We explore the possibilities that the source is a SMBH binary or a post-merger recoiling SMBH. We place constraints on a possible SMBH companion using observations taken with the NRAO Very Large Array. If a companion SMBH can be confirmed, this system could be a future GW source detectable with pulsar timing.

In order to detect such sources, our pulsar timing array must be as sensitive as possible, requiring the mitigation of all other astrophysical delays, including those from the interstellar medium (ISM). Using NANOGrav wideband multi-frequency observations obtained with the Green Bank Telescope and Arecibo Observatory, we characterize frequency-dependent dispersion. This effect is quantified by the dispersion measure (DM). We analyze trends in the DM time series, propose sources of these trends, and identify timescales over which the DM varies beyond measurement errors and therefore can no longer be modeled as constant in timing. Analyzing DM variations aids in characterizing properties of the ISM and informs our timing observation strategy.

Multi-telescope observations around the globe and at complementary frequencies can be used to more sensitively constrain DMs. We compare DMs measured with dual-frequency observations obtained using the Giant Metrewave Radio Telescope (GMRT) to those calculated in the NANOGrav 11-year data release to assess the possible precision of frequency-dependent noise measurements with the GMRT. We discuss the possibility of incorporating the GMRT into international pulsar timing efforts and anticipated challenges in future data combination.

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