Constraints on the Emission Geometries of Gamma-ray Millisecond Pulsars Observed with the Fermi Large Area Telescope

Abstract

Millisecond pulsars (MSPs) have been established as a class of high-energy ($\ge$0.1 GeV) emitters with the Large Area Telescope (LAT) aboard the \emph{Fermi Gamma-ray Space Telescope}. Most MSP gamma-ray light curves display sharp peaks indicative of thin accelerating gaps, suggesting copious pair-creation in the open volume. MSP gamma-ray and radio light curves have been simulated using geometric outer-gap (OG), slot-gap/two-pole caustic (TPC), and pair-starved polar cap gamma-ray models and either a hollow-cone beam or altitude-limited, outer-magnetospheric gap radio model, all assuming a vacuum retarded dipolar magnetic field geometry. A Markov chain Monte Carlo maximum likelihood technique has been developed to find the best-fit model parameters for nineteen MSPs using data from the LAT and various radio observatories. The best-fit viewing angles follow a uniform, angular distribution. The distribution of magnetic inclination angles favors all angles equally, contrary to analyses of non-recycled pulsars, which supports the theory that MSPs have been spun-up via accretion. There are suggestions that the radio emission should occur nearer the light cylinder. These results have implications for MSP population simulations and for addressing MSP contributions to diffuse backgrounds. An implied transition in the gamma-ray luminosity versus spin-down power trend is observed but more statistics are necessary to describe it.

arXiv commentThesis in partial fulfilment of requirement for Doctor of Philosophy, defended April 2011, degree awarded May 2011, Department of Physics, University of Maryland, College Park, MD. Only change from submitted version is use of single spaced text instead of double spaced

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• Constraints on the Emission Geometries and Spin Evolution of Gamma-ray Millisecond Pulsars
• Six millisecond pulsars detected by the Fermi Large Area Telescope and the radio/gamma-ray connection of millisecond pulsars
• On the non-detection of gamma-rays from energetic millisecond pulsars -- dependence on viewing geometry
• Modeling the Pulse Profiles of Millisecond Pulsars in the Second LAT Catalog of gamma-ray Pulsars