Hope College Physics Department
Research Experiences for Undergraduates
Summer 2009
Project Summary

 

Project Title: Pulsar Population Statistics in the Fermi Era
Student Name: Erin Nagelkirk
Student's Home Institution: Wayne State University
Research Advisor: Dr. Peter Gonthier
Source of Support: This material is based upon work supported by the National Science Foundation under NSF-REU Grant No. PHY-0452206, Michigan Space Grant Consortium, and the National Aeronautics and Space Administration Astrophysics Theory and Fundamental Physics Program 08-ATFP08-0130.

Since the launch of the Fermi Gamma-ray Space Telescope in June 2008, Fermi has discovered more gamma-ray pulsars than the six (with good statistics) discovered during the nine years of observation by its predecessor EGRET aboard the Compton Gamma-ray Observatory. The new gamma-ray pulsar catalogue, soon to be made public, will contain 23 young radio pulsars, 16 radio-weak pulsars, and 8 millisecond pulsars newly discovered by Fermi. Contrary to expectation from previous studies, the gamma-ray emission appears to originate high in the neutron star magnetosphere where two high-energy emission models compete – the polar cap slot gap and the outer gap models. In order to simulate these new Fermi pulsars, we had to make extensive modification to our Monte Carlo population statistics code that we have used earlier. These improvements included newly generate high altitude slot gap phase plot maps that portray the all sky gamma-ray emission intensity, a new normalization prescription for these phase plots, incorporate the outer gap model, and newly simulated Fermi threshold all-sky map by the Fermi team at Saclay, France, who found that the spectral characteristics of pulsars have significant implications for the detection sensitivity of the Large Area Telescope (LAT) aboard Fermi. While very different physical mechanisms are involved in these high-energy models, our simulations suggest very similar light curves and statistics are obtained for both models. However, clear signatures are seen in the statistics of parameters associated with the viewing geometry. Unfortunately, the viewing angles obtained from X-ray emission patterns of pulsar wind nebulae at the present do not fully discriminate between the high-altitude emission of the slot gap and outer gap models. We are now in a position to study the correlations between the light curves of radio and gamma-ray emission beams with our code to help establish the location of the particle acceleration in the magnetosphere. __________________________________________________________________________________________________________________________
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