Synchrotron Spectral Curvature from 22 MHz to 23 GHz

TL;DR

This study combines radio sky surveys from 22 MHz to 23 GHz to analyze the spectral curvature of diffuse Galactic synchrotron emission, revealing a steepening spectrum with frequency and constraining models of cosmic ray electrons.

Contribution

It provides a comprehensive spectral characterization of Galactic synchrotron emission across a broad frequency range, extending previous models to higher frequencies.

Findings

Spectral index at 23 GHz is consistent with previous measurements.

The spectrum steepens by 0.07 per octave in frequency.

No spectral break is observed below 23 GHz.

Abstract

We combine surveys of the radio sky at frequencies 22 MHz to 1.4 GHz with data from the ARCADE-2 instrument at frequencies 3 to 10 GHz to characterize the frequency spectrum of diffuse synchrotron emission in the Galaxy. The radio spectrum steepens with frequency from 22 MHz to 10 GHz. The projected spectral index at 23 GHz derived from the low-frequency data agrees well with independent measurements using only data at frequencies 23 GHz and above. Comparing the spectral index at 23 GHz to the value from previously published analyses allows extension of the model to higher frequencies. The combined data are consistent with a power-law index beta = -2.64 +/- 0.03 at 0.31 GHz, steepening by an amount Delta beta = 0.07 every octave in frequency. Comparison of the radio data to models including the cosmic ray energy spectrum suggests that any break in the synchrotron spectrum must occur at frequencies above 23 GHz.