Hope College Department of Physics and Engineering
Research Experiences for Undergraduates
Summer 2004
Project Summary

 

Project Title: Constraining the Viewing Geometry of Radio Pulsars
Student Name(s): Brenna Giacherio and Sarah Story
Student Home Institution: Hope College
Research Advisor(s): Dr. P.L Gonthier
Source of Support: Michigan Space Grant Consortium, REU

This particular project investigates the viewing geometry of radio pulsars. The viewing geometry how we see the pulsar from Earth is defined by two angles: alpha, the angle between the rotational and magnetic axes, and beta, the angle between the magnetic axis and our line of sight. We are assuming two beams of radio emission from the polar cap: core and cone. These are both Gaussian in shape as proposed by Arzoumanian, Chernoff, and Cordes (2002). In addition, we are assuming frequency dependence on characteristic widths of the beams and the nested conal structure of Mitra and Deshpande (1999). We used a program written in Igor Pro to fit single, double, and triple-peak pulsars with good polarization data. Our focus was on pulsars with three peaks, which provide the best way to constrain the viewing geometry. The raw data used in the fitting was obtained from the European Pulsar Network (EPN) database. We fit as many frequencies with reasonable data as we could find for each pulsar. The more frequencies we had, the more confident we could be with the determined viewing geometry and the better could trends be fit to the data. Along with the viewing geometry were seven other variable values, obtained during the fit of the pulsar, which were used to fit trends. Many of the fits crashed when the variables were released in Igor. These had to be manually fit by keeping the variables fixed and carefully tweaking them. A total of sixty-seven pulsars were fit with varying numbers of frequencies.


 

Project Title: Developing Radio Beam Geometry And Luminosity Models Of Pulsars
Student Name(s): Sarah Story and Brenna Giacherio
Student Home Institution: Hope College
Research Advisor(s): Dr. P.L Gonthier
Source of Support: Michigan Space Grant Consortium, REU

Our recent studies of pulsar population statistics suggest that improvements of radio and gamma-ray beam geometry and luminosity models require further refinement. The polarization properties of radio profiles of gama-ray pulsars do not suggest that short period pulsars are core dominated, as discussed by the study of Arzoumanian, Chernoff & Cordes (2002). Furthermore, the predicted radio luminosity in this model seems to be too large compared to those required by the simulations. The goal of this project is to constrain the viewing geometry for some radio pulsars, especially three-peaked pulse profiles, in order to limit the uncertainty of the magnetic inclination and impact angles. We perform fits of the pulse profile and position angle sweep of radio pulsars for the available frequencies. We obtain separate spectral indices for the core and cone beams and explore the trends of the ratio of core to cone peak fluxes and luminosities. We will present our current findings and implications.