2001A&A...372..627K

We present radio maps of the historical supernova remnant G11.2-0.3 in the frequency range from 4.85GHz to 32GHz. The integrated spectrum with α=-0.50 (S~ν^α) is dominated by its steep spectrum shell emission (α~-0.57), although a flat spectrum core structure classifies G11.2-0.3 as a composite supernova remnant. A radial magnetic field structure is observed. An analysis of the multi-frequency polarization data results in highly varying rotation measures along the shell. The percentage polarization is rather low (∼2%) and we conclude that G11.2-0.3 is in the transient phase from free to adiabatic expansion. The central flat spectrum component is partly resolved. A compact radio source with an inverted spectrum likely coincides with the previously detected X-ray pulsar (Torii et al., 1997ApJ...489L.145T). Two symmetric structures with flat radio spectra possibly indicate a bipolar outflow. Combining available X-ray and radio data we conclude that G11.2-0.3 is likely the remnant of a type II supernova explosion with an early type B progenitor star.