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Long-Term Timing of Pulsars in NGC 6440: An Updated Mass Limit of Millisecond Pulsar J1748-2021B

Clifford, Nick
Thesis/Dissertation; Online
Clifford, Nick
Ransom, Scott
After 11 years of continued observations with the Green Bank Telescope (GBT), we present updated timing solutions of 6 previously published pulsars in NGC 6440. We obtain improvements in timing parameters that allow us to better describe the dynamics of the cluster, such as measure the proper motion of the pulsars and and estimate the cluster’s motion (μα=−1.04(20) mas yr−1, μδ=−3.0(2.5) mas yr−1). Using additional observing bandwidth, we measure the flux densities and spectral indices of each pulsar and investigate the effects of refractive scintillation on the variance of each pulsar’s flux density as a function of observing frequency. For the eccentric binary millisecond pulsar (MSP) NGC 6440B, we report on a much more precise rate of periastron advance, ̇ω= 0.003684(21)◦yr−1, which if purely relativistic, would indicate a total system mass of 2.675±0.022 and a median pulsar mass of 2.548+0.047−0.078M assuming random inclinations. We also measure the rate of periastron advance for NGC 6440F ( ̇ω= 0.0673(28)◦yr−1) despite its incredibly low flux density (S1.5= 0.019 mJy).
University of Virginia, Department of Astronomy, BS (Bachelor of Science), 2019
Published Date
BS (Bachelor of Science)
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