Oscillation Maps in the Broadband Radio Spectrum of the 1 August 2010 Event

TL;DR

This study introduces a novel wavelet-based oscillation mapping technique across the radio spectrum, revealing specific wave periods and phase behaviors associated with solar coronal waves during a 2010 solar event.

Contribution

It presents a new method for constructing oscillation maps in the radio spectrum and links observed radio oscillations to UV wave phenomena and electron beam modulation.

Findings

Oscillation with 181s period detected across 25-2000 MHz spectrum.

Periods of 69 and 40s confirmed in 250-870 MHz range.

Phase analysis suggests UV wave influence and electron beam modulation.

Abstract

We search for indications of waves in the 25-2000 MHz radio spectrum of the 1 August 2010 event (SOL2010-08-01T08:57:00L075C013), where fast propagating waves in the solar corona with the periods of 181, 69, and 40 seconds were detected in UV observations. Using the wavelet technique we construct a new type of map of oscillations for selected periods in the whole domain of the radio spectrum. While the oscillation with the period of 181 seconds was recognized in the whole 25-2000 MHz radio spectrum, oscillations with periods of 69 and 40 seconds were confirmed only in the 250-870 MHz frequency range. In the 800-2000 MHz range we found periods of 50 and 80 seconds. Moreover, in the 250-870 MHz frequency range, the oscillation with the period of about 420 seconds was detected. We also made maps of phases of the 181-second oscillations in order to analyze their frequency drift. At the beginning of the radio event, in the 2000-500 MHz frequency range the phase of the 181-second oscillation drifts towards lower frequencies. On the other hand, at frequencies 25-500 MHz we found that the phase is nearly synchronous. While the phase drift at higher frequencies can be interpreted as being caused by the UV wave, the synchronization of the phase on lower frequencies is explained by the fast-electron beams, whose acceleration is modulated by the UV wave. Owing to this modulation, the electron beams are accelerated with the period of the UV wave (181 seconds). These beams propagate upwards through the solar corona and generate the 25-500 MHz radio emission with the 181-second period. Due to high beam velocity (~c/3, where c is the light speed) the 25-500 MHz radio emission, corresponding to a large interval of heights in the solar corona, is nearly synchronous.