Fast magnetoacoustic waves in a fan structure above the coronal magnetic null point

TL;DR

This study uses high-cadence radio observations and magnetic field modeling to detect fast magnetoacoustic waves propagating in a fan structure above a coronal magnetic null point during a solar flare.

Contribution

It provides the first evidence of fast magnetoacoustic waves in a fan structure near a coronal null point using radio wave analysis and wavelet techniques.

Findings

Detection of wavelet tadpoles indicating magnetoacoustic waves

Radio sources located in fan structure of magnetic null point

Plasma parameters consistent with wave propagation scenario

Abstract

We analyze the 26 November 2005 solar radio event observed interferometrically at frequencies of 244 and 611 MHz by the Giant Metrewave Radio Telescope (GMRT) in Pune, India. These observations are used to make interferometric maps of the event at both frequencies with the time cadence of 1 s from 06:50 to 07:12 UT. These maps reveal several radio sources. The light curves of these sources show that only two sources at 244 MHz and 611 MHz are well correlated in time. The EUV flare is more localized with flare loops located rather away from the radio sources. Using the SoHO/MDI observations and potential magnetic field extrapolation we demonstrate that both the correlated sources are located in the fan structure of magnetic field lines starting from a coronal magnetic null point. Wavelet analysis of the light curves of the radio sources detects tadpoles with periods in the range P = 10-83 s. These wavelet tadpoles indicate the presence of fast magnetoacoustic waves that propagate in the fan structure of the coronal magnetic null point. We estimate the plasma parameters in the studied radio sources and find them consistent with the presented scenario involving the coronal magnetic null point.