A high frequency radio study of G11.2-0.3, a historical supernova remnant with a flat spectrum core

¹ National Research Council, Herzberg Institute of Astrophysics, Dominion Radio Astrophysical Observatory, PO Box 248, Penticton, British Columbia, V2A 6K3, Canada
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: wreich@mpifr-bonn.mpg.de

Corresponding author: R. Kothes, roland.kothes@hia.nrc.ca

Received: 30 January 2001
Accepted: 19 March 2001

Abstract

We present radio maps of the historical supernova remnant G11.2-0.3 in the frequency range from 4.85 GHz to 32 GHz. The integrated spectrum with () is dominated by its steep spectrum shell emission (), 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. [CITE]). 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.