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M. G. Baring (Rice University)
The rapid increase in observational data on soft gamma repeaters (SGRs) over the last few years has included the revelation of quiescent non-thermal X-ray emission at levels that are very intense for neutron stars. While dwarfed by the flare and giant flare activity, this component nevertheless has important implications for our understanding of the SGR environment. In quiescence, it is possible that SGRs can emit in a pulsar-like mode, even if the power is not of a rotational origin. A principal candidate for such emission is inverse Compton scattering in the strongly fields of the SGR magnetosphere, since it is believed to dominate over other primary emission mechanisms in high field pulsars. This paper determines expectations for such emission spectra, formed from non-thermal electrons accelerated in a pulsar-like polar cap potential upscattering thermal X-rays from the hot stellar surface. It is found that the X-ray portion of the spectrum is moderately steep for a narrow band, not unlike that observed in magnetars. This flattens into a very flat soft gamma-ray continuum with spectral structure that depends on observational perspective. Observational flux constraints on this pulsar component are presented, leading to the identification of diagnostics on the emission geometry.
This work was sponsored by the NASA Astrophysics Theory Program.