EVLA Observations of Galactic Supernova Remnants: Wide-field Continuum and Spectral-index Imaging

TL;DR

This paper demonstrates the EVLA's capability for wide-field, high-resolution continuum and spectral index imaging, enabling better differentiation of thermal and non-thermal emission in Galactic supernova remnants through simultaneous wide-band observations.

Contribution

It introduces new wide-band, wide-field imaging algorithms and applies them to EVLA data, improving the interpretation of complex Galactic radio emission regions.

Findings

Successful imaging of a large SNR G55.7+3.4 with wide-field sensitivity.

Spectral index maps differentiate thermal and non-thermal emission regions.

Validation of EVLA's wide-field wide-band imaging capabilities.

Abstract

The radio continuum emission from the Galaxy has a rich mix of thermal and non-thermal emission. This very richness makes their interpretation challenging since the low radio opacity means that a radio image represents the sum of all emission regions along the line-of-sight. These challenges make the existing narrow-band radio surveys of the Galactic plane difficult to interpret: e.g. a small region of emission might be a supernova remnant (SNR) or an HII region, or a complex combination of both. Instantaneous wide bandwidth radio observations in combination with the capability for high resolution spectral index mapping, can be directly used to disentangle these effects. Here we demonstrate simultaneous continuum and spectral index imaging capability at the full continuum sensitivity and resolution using newly developed wide-band wide-field imaging algorithms. Observations were done in the L- and C-Band with a total bandwidth of 1 and 2 GHz respectively. We present preliminary results in the form of a full-field continuum image covering the wide-band sensitivity pattern of the EVLA centered on a large but poorly studied SNR (G55.7+3.4) and relatively narrower field continuum and spectral index maps of three fields containing SNR and diffused thermal emission. We demonstrate that spatially resolved spectral index maps differentiates regions with emission of different physical origin (spectral index variation across composite SNRs and separation of thermal and non-thermal emission), superimposed along the line of sight. The wide-field image centered on the SNR G55.7+3.4 also demonstrates the excellent wide-field wide-band imaging capability of the EVLA.