Measuring the diffuse Galactic synchrotron spectral index and curvature between 45 and 2300 MHz

TL;DR

This paper creates an all-sky map of Galactic synchrotron spectral index and curvature from 45 to 2300 MHz, improving model accuracy and consistency over existing models.

Contribution

It introduces a new parametric, least-squares method for estimating synchrotron emission, validated against external datasets, with publicly available results.

Findings

Our model achieves about 20% accuracy compared to empirical data.

It outperforms existing models like pysm3 and GSM in consistency and reliability.

The results are publicly accessible for further research.

Abstract

We present an all-sky map of the synchrotron spectral index and curvature between 45 and 2300 MHz at a resolution of 1 degree calculated from a combination of numerous partial sky empirical measurements. We employ a least-squares parametric fit which relies on removing a free-free emission template and a component separation technique which fits for both synchrotron and free-free emission. We compare our diffuse sky model estimates against those derived from the models widely used in the community (e.g. pysm3 and GSM) employing external datasets that were not included in the estimation process. Our evaluation focuses on identifying the enhanced consistency at both the map level and in pixel-to-pixel correlations, allowing for a more robust verification of our model's performance. We find our parametric, least-squares synchrotron estimate to be the most reliable across radio frequencies as it consistently provides sky models with average accuracies (when compared to empirical data) of around 20 per cent, whilst other model performances range on average between 10 and 70 per cent accurate. The results obtained have been made publicly accessible online and can be utilized to further develop and refine models of Galactic synchrotron emission.