The Monoceros supernova remnant (SNR G205.5+0.5) is a large shell-type SNR located in the Rosette molecular complex and thought to be interacting with the Rosette Nebula. We aim to re-examine the radio spectral index and its spatial variation over the Monoceros SNR as well as study its properties of evolution within the complex interstellar medium. We extracted radio continuum data for the Monoceros complex region from the Effelsberg 21cm and 11cm surveys and the Urumqi 6 cm polarization survey. We used the new Arecibo GALFA-HI survey data with much higher resolution and sensitivity than that previously available to identify the HI shell related with the SNR. Multi-wavelengths data are included to investigate the properties of the SNR. The spectral index α (Sν∝να) averaged over the SNR is -0.41±0.16. The TT-plots and the distribution of α over the SNR show spatial variations that steepen toward the inner western filamentary shell. Polarized emission is prominent on the western filamentary shell region. The RM there is estimated to be about 30±77n*rad/m2, where the n=1 solution is preferred, and the magnetic field has a strength of about 9.5µG. From the HI channel maps, further evidence is provided for an interaction between the Monoceros SNR and the Rosette Nebula. We identify partial neutral hydrogen shell structures in the northwestern region at velocities of +15km/s circumscribing the continuum emission. The HI shell has swept up a mass of about 4000M☉ for a distance of 1.6kpc. The western HI shell, well associated with the dust emission, is found to lie outside of the radio shell. We suggest that the Monoceros SNR is evolving within a cavity blown out by the progenitor and has triggered part of the star formation in the Rosette Nebula. The Monoceros SNR is interacting with the ambient interstellar medium with ultra-high energy emission detected. Its interaction with the Rosette Nebula is further supported by new evidence from HI data, which will help the investigation of the emission mechanism of the high-energy emission.
ISM: supernova remnants - polarization - radio continuum: general - methods: observational
Paragraph 1. H II region G206.35+1.35 not identifed. Paragraph 2.1 HII region 0641+06 is LBN 206.29+01.55 in Simbad.