Solar Energetic Particle Spectrum on 13 December 2006 Determined by   IceTop
  On 13 December 2006 the IceTop air shower array at the South Pole detected a major solar particle event. By numerically simulating the response of the IceTop tanks, which are thick Cherenkov detectors with multiple thresholds deployed at high altitude with no geomagnetic cut-off, we determined the particle energy spectrum in the energy range 0.6 to 7.6 GeV. This is the first such spectral measurement using a single instrument with a well defined viewing direction. We compare the IceTop spectrum and its time evolution with previously published results and outline plans for improved resolution of future solar particle spectra. 
R. Abbasi (for the IceCube Collaboration)