Imaging of SNR IC443 and W44 with the Sardinia Radio Telescope at 1.5 and 7 GHz

Abstract

Observations of supernova remnants (SNRs) are a powerful tool for\ninvestigating the later stages of stellar evolution, the properties of the\nambient interstellar medium, and the physics of particle acceleration and\nshocks. For a fraction of SNRs, multi-wavelength coverage from radio to ultra\nhigh-energies has been provided, constraining their contributions to the\nproduction of Galactic cosmic rays. Although radio emission is the most common\nidentifier of SNRs and a prime probe for refining models, high-resolution\nimages at frequencies above 5 GHz are surprisingly lacking, even for bright and\nwell-known SNRs such as IC443 and W44. In the frameworks of the Astronomical\nValidation and Early Science Program with the 64-m single-dish Sardinia Radio\nTelescope, we provided, for the first time, single-dish deep imaging at 7 GHz\nof the IC443 and W44 complexes coupled with spatially-resolved spectra in the\n1.5-7 GHz frequency range. Our images were obtained through on-the-fly mapping\ntechniques, providing antenna beam oversampling and resulting in accurate\ncontinuum flux density measurements. The integrated flux densities associated\nwith IC443 are S_1.5GHz = 134 +/- 4 Jy and S_7GHz = 67 +/- 3 Jy. For W44, we\nmeasured total flux densities of S_1.5GHz = 214 +/- 6 Jy and S_7GHz = 94 +/- 4\nJy. Spectral index maps provide evidence of a wide physical parameter scatter\namong different SNR regions: a flat spectrum is observed from the brightest SNR\nregions at the shock, while steeper spectral indices (up to 0.7) are observed\nin fainter cooling regions, disentangling in this way different populations and\nspectra of radio/gamma-ray-emitting electrons in these SNRs.\n