Population Studies of Radio and Gamma-ray Normal Pulsars
Dr. Peter Gonthier
Dr. Alice Harding, NASA Goddard Space Flight Center
We present the preliminary results of the latest population synthesis of radio and gamma-ray normal pulsars from the Galactic disk. The Fermi Second Pulsar Catalogue has provided over eighty gamma-ray normal pulsars that can be used to improve and constrain current emission models. We use a Markov Chain Monte Carlo method to create cumulative distributions of radio and gamma-ray pulsar characteristics to compare to measured distributions. Empirical radio and gamma-ray luminosity models are included that are period and period derivative dependent with freely varying exponents. During the simulation, the period and period derivative exponents as well as the magnitudes of model luminosities are varied to reproduce the number and birth rates of normal pulsars in the Galaxy. The simulation is normalized to the number of radio pulsars detected in ten radio surveys. Recent studies suggesting the necessity of magnetic field decay have motivated the implementation of a magnetic field decay model, similar in character to the model used in our previous studies. This addition has improved the funnel shape of radio pulsars in the period derivative – period diagram, however none of our changes were able replicate the group of young high period, high period derivative normal pulsars seen by Fermi. The latest model was also able to improve the overall age of Fermi gamma-ray pulsars, but the simulated distribution has a wider range over the period than the observed distribution. The enigma remains of not being able to account for both Fermi and radio pulsars from the same group of present-day neutron stars with the same birth characteristics. We intend to focus our future effort on addressing this issue.
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