Modeling Emission and Particle Acceleration in Magnetars

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The research to be conducted centers on the properties of magnetars - a subclass ofneutron stars with magnetic fields of strength in excess of the critical quantumelectrodynamic threshold. Here, a series of projects will be carried out aimed at helpinganswer several questions of current scientific interest. Included are: (1) What is theemission mechanism of magnetars in quiescence? (2) What controls the spectrum of softgamma ray repeater (a type of magnetar) flares? (3) How is the energy of activity ofmagnetars tapped in their magnetospheres? And (4) physically, how and why aremagnetars different from conventional pulsars? Three general avenues of research will beundertaken, each with associate subprojects. The first is an investigation of resonantscattering in shaping the spectrum of anomalous x-ray pulsar spectra by refiningcalculations of resonant Compton scattering in ultra strong magnetic fields and theupscattering of thermal surface photons by magnetospheric electrons. In the second, theroles of resonant Compton scattering and photon splitting in the burst spectra of softgamma-ray repeaters will be explored. This includes developing dispersion and selectionrules for photon splitting in ultra strong magnetic fields. Finally, a generalized formalismfor stochastic, diffusive, gyroresonant acceleration of particles due to magneticturbulence superposed upon the global magnetar field structure will be developed. Amajor emphasis will be determining the shape of the non-thermal distribution and howthe maximum energy of acceleration couples to environmental parameters, which will inturn lead to useful observational diagnostics on the emission region.A graduate student will be employed and trained and will be an integral part of the work.This student will also be exposed to undergraduate pedagogy by teaching at least twolectures per year on neutron stars. Undergraduates are expected to contribute as wellthrough small, well defined tasks. Results of this work will be presented to the publicthrough outreach activities at local high schools and through the Houston AstronomicalSociety.