Faculty Mentor(s)

Dr. Peter Gonthier

Document Type


Event Date



Telescopes including RXTE, INTEGRAL, Suzaku, and Fermi have detected steady non-thermal X-ray emission in the 10 - 200 keV band from strongly magnetic neutron stars known as magnetars. Magnetic inverse Compton scattering is believed to be a leading mechanism for the production of this intense X-ray radiation. Generated by electrons possessing ultra-relativistic energies, this leads to attractive simplifications of the magnetic Compton cross section. We recently addressed such a case by developing compact analytic expressions using correct spin-dependent widths acquired through the implementation of Sokolov & Ternov (ST) basis states, focusing specifically on ground state-to-ground state scattering. Such scattering in magnetar magnetospheres can cool electrons down to mildly-relativistic energies. Moreover, soft gamma-ray flaring in magnetars may well involve strong Comptonization in expanding clouds of mildly-relativistic pairs necessitating the development of more general magnetic scattering cross sections, where the incoming photons acquire substantial incident angles relative to the magnetic field of the magnetar in the rest frame of the electron, with the intermediate state being excited to arbitrary Landau levels. Throughout this research, we highlight results from such a generalization using ST formalism. The cross sections treat the plethora of harmonic resonances associated with various cyclotron transitions between Landau states. The Compton cross section is developed for photon polarization dependence and includes the correct spin dependent widths. Comparing correct QED cross section to the traditional nonrelativistic magnetic Thomson cross section, it is apparent that these lead to significantly different results, especially near the resonance peak demonstrating the necessity to develop the correct formulism of the Compton cross section in strong magnetic fields using correct spin-dependent widths of the resonances.


This work is supported by the National Science Foundation (grants AST-1009731 and REU PHY/DMR-1004811), the NASA Astrophysics Theory Program grant NNX09AQ71G, and the Michigan Space Grant Consortium.