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D. Marsden (NASA/GSFC), R. E. Lingenfelter, R. E. Rothschild (UCSD), J. C. Higdon (Claremont Colleges)
Soft gamma-ray repeaters (SGRs) and anomalous x-ray pulsars (AXPs) are a young (~104 year old) yet slowly spinning (P~10 s) population of radio-quiet Galactic neutron stars with unusual spectral and temporal characteristics. By studying the supernova remnants associated with these objects, we find that the SGR and AXP progenitor stars preferentially exploded in the dense (>0.1 cm-3) phase of the interstellar medium, which is highly unusual for young neutron stars and contrary to the predictions of models in which the properties of these sources are due to superstrong neutron star magnetic fields. Instead, we argue that SGRs and AXPs are likely formed as a result of interactions between the (high velocity) neutron stars and co-moving ejecta from their parent supernovae.