Ignasi Reichardt, Emma de Oña Wilhelmi, Javier Rico, Ruizhi Yang
We analyse 3.5 years of public Fermi/LAT data around the position of the supernova remnant HB 21, where four point-like sources from the 2nd Fermi/LAT catalog are found. We detect an extended gamma-ray source coincident with the shell observed at radio wavelengths. The morphological modelling favours a uniform circle as best template for the observed emission. The spectral energy distribution is best described by a curved power law, with a maximum at $0.413\pm0.019$\,GeV. Dividing the circle in three regions coincident with previously identified shocked molecular clouds, we find indications that one of this regions has a softer spectrum. Combining this information with the morphology above 3\,GeV, we suggest that the gamma-ray emission from HB 21 can be understood as a combination of emission from the shell itself plus emission from shocked/illuminated molecular clouds.
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http://arxiv.org/abs/1207.2057
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