High Spectral Resolution Observation of Decimetric Radio Spikes Emitted by Solar Flares - First Results of the Phoenix-3 Spectrometer

TL;DR

This paper introduces the Phoenix-3 spectrometer capable of high spectral resolution solar radio observations, presenting initial findings on narrowband spike characteristics during solar flares.

Contribution

First implementation of Phoenix-3 spectrometer providing unprecedented spectral resolution for solar radio emissions and initial analysis of spike bandwidths and spectral features.

Findings

Spike bandwidths follow a power-law distribution, dropping below 2 MHz.

Narrowest spikes have FWHM less than 0.3 MHz, near natural maser emission width.

Spike spectra are asymmetric with a low-frequency tail.

Abstract

A new multichannel spectrometer, Phoenix-3, is in operation having capabilities to observe solar flare radio emissions in the 0.1 - 5 GHz range at an unprecedented spectral resolution of 61.0 kHz with high sensitivity. The present setup for routine observations allows measuring circular polarization, but requires a data compression to 4096 frequency channels in the 1 - 5 GHz range and to a temporal resolution of 200 ms. First results are presented by means of a well observed event that included narrowband spikes at 350 - 850 MHz. Spike bandwidths are found to have a power-law distribution, dropping off below a value of 2 MHz for full width at half maximum (FWHM). The narrowest spikes have a FWHM bandwidth less than 0.3 MHz or 0.04% of the central frequency. The smallest half-power increase occurs within 0.104 MHz at 443.5 MHz, which is close to the predicted natural width of maser emission. The spectrum of spikes is found to be asymmetric, having an enhanced low-frequency tail. The distribution of the total spike flux is approximately an exponential.